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73-474: (Redirected from Dial Tones ) dial tone is a tone on a phone indicating that the line is operational Dial Tone (G.I. Joe) Dial Tones, fictional band in Happy Days (musical) "Dial Tones", song by As It Is from the album Never Happy, Ever After Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with

146-497: A 100 Hz beat frequency. Most of Europe , as well as much of Latin America and Africa , uses a constant single tone of 425 Hz. France currently uses a single 440 Hz tone and Japan uses a single 400 Hz tone. Cellular telephone services do not generate dial tones as no connection is made until the entire number has been specified and transmitted. Private branch exchanges (PBXs) or key telephone systems also play

219-530: A 50 Hz dial tone. The modern dial tone varies between countries. The Precise Tone Plan for the North American Numbering Plan of the US , Canada , and various Caribbean nations specifies a combination of two tones (350 Hz and 440 Hz) which, when mixed, creates a beat frequency of 90 Hz. The UK dial tone is similar, but combines 350 Hz and 450 Hz tones instead, creating

292-468: A NANP number is rendered as +1NPANXXXXXX , without spaces or punctuation, e.g. +12505550199 . The plus sign indicates that the user may have to dial another prefix per local dialing conventions in the country of origin that selects a trunk for international network access; the digits immediately following are thus the country code, where 1 is the NANP country code. The North American Numbering Plan recognizes

365-472: A dial tone to station users. It may be the same type as used by the public switched telephone network (PSTN), or it may be a different tone to remind users to dial a prefix or select by another method an outside line. A secondary dial tone is a dial tone-like sound presented to the caller after a call has been set up to prompt for additional digits to be dialed. Secondary dial tones are often used in call queuing and call forwarding systems. A stutter dial tone

438-528: A fictional number, could be rendered as 250-555-0199, (250) 555-0199, 250-5550199, or 250/555-0199. The parentheses were originally used to indicate that the area code was not necessary for local dialing. The Government of Canada's Translation Bureau recommends using hyphens between groups; e.g. 250-555-0199. Using the global formatting for telephone numbers, per recommendation E.164 by the International Telecommunication Union (ITU),

511-620: A part of the area retained a single code while the rest of the region received an overlay code. The only service-specific overlay in the NANP was area code 917 (New York City) when it was first installed; such service-specific area code assignments were later prohibited by the Federal Communications Commission. Most area codes of the form N10, originally reserved for AT&T's Teletypewriter eXchange (TWX) service, were transferred to Western Union in 1969 and were freed for other use in 1981 after conversion to Telex II service

584-476: A result, New York state was initially divided into five areas, the most of any state. Illinois , Ohio , Pennsylvania , and Texas were assigned four NPAs each, and California , Iowa , and Michigan received three. Eight states and provinces were divided into two NPAs. Traditionally, central office switching systems were designed to serve as many as ten thousand subscriber numbers. Thus, subscribers were assigned four-digit line or station numbers. This rounded

657-448: A result, a few North American telephone administrations, notably New York Telephone Co., first introduced letter combinations that could not be associated with a familiar pronounceable central office name. Finally, they sought the elimination of central office names and letter codes, and introduced all-number calling (ANC). With all-number calling, the number of permissible central office prefixes increased from 540 to potentially 800, but

730-459: A standard facility with the cutover of the 7A Rotary Automatic Machine Switching System at Darlington, England, on 10 October 1914. Dial tone was an essential feature, because the 7A Rotary system was a common control switching system. It used the dial tone to indicate to the user that the switching system was ready to accept digits. In the United States, dial tone was introduced in the 1920s. By

803-407: A three-digit telephone number prefix, commonly termed the area code . Each telephone is assigned a seven-digit telephone number unique only within its respective numbering plan area. The telephone number consists of a three-digit central office (or exchange ) code and a four-digit station number. The combination of an area code and the telephone number serves as a destination routing address in

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876-606: Is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean . This group is historically known as World Zone 1 and has the telephone country code 1 . Some North American countries, most notably Mexico , do not participate with the NANP. The concepts of the NANP were devised originally during the 1940s by the American Telephone and Telegraph Company (AT&T) for

949-406: Is a rapidly interrupted tone used to indicate special service conditions. It may serve as a message-waiting indicator for voice mail, or indicate that a calling feature , such as call forwarding has been activated. A soft dial tone or express dial tone may be used when no actual service is active on a line, and normal calls cannot be made. It is maintained only so that an attached phone can dial

1022-413: Is essentially a single pulse of loop interruption, was automatically ignored by most switching equipment of the time. Therefore, the 0/1 rule for the area code provided a convenient means to distinguish seven-digit dialing from ten-digit dialing. The use of telephone exchange names as part of telephone numbers had been a well-established practice, and this was preserved for convenience and expediency in

1095-556: Is used for non-geographic applications. Area code 900 has been used for high-toll 900 numbers . The North American Numbering Plan does not reserve special non-geographic area codes exclusively for cellular phones , as is customary in some other national telephone administrations. Only one regional exception exists in area code 600 in Canada. For cellular services, telephone numbers in the NANP are allocated within each area code from special central office prefixes. Calls to them are billed at

1168-576: The Bell System and the independent telephone companies in North America in Operator Toll Dialing . The first task was to unify the diverse local telephone numbering plans that had been established during the preceding decades, with the goal to speed call completion times and decrease the costs for long-distance calling , by reducing manual labor by switchboard operators . Eventually, it prepared

1241-752: The British Empire and their continued associations with Canada, especially during the years of the telegraph and the All Red Line system. Not all North American polities participate in the NANP. Exceptions include Mexico, Greenland , Saint Pierre and Miquelon , the Central American countries and some Caribbean countries ( Cuba , Haiti , the French Caribbean and the Dutch Caribbean , except for Sint Maarten ). The only Spanish-speaking places in

1314-541: The Indiana numbering plan area 317 was divided to provide a larger numbering pool in the Indiana suburbs of Chicago ( area code 219 ). Initially, states divided into multiple numbering plan areas were assigned area codes with the digit 1 in the second position, while areas that comprised entire states or provinces received codes with 0 as the middle digit. This rule was violated by the early 1950s, as NPAs with digit 0 in

1387-515: The area code 809 as early as 1958 by the administrators at AT&T, individual participating countries or territories had no autonomy over their numbering plan as they received centrally assigned central office prefixes that needed to be unique from those of other countries with the same area code. Regions in Mexico with high call volumes to and from the US were assigned functional area codes as early as 1963, for

1460-462: The emergency telephone number (such as 911 , 112 or 999 ), in compliance with the law in most places. It can sometimes also call the business office of the local exchange carrier which owns or last leased the line, such as via 6-1-1 . Other functions such as ringback or ANAC may also be accessed by technicians in order to facilitate installation or activation. North American Numbering Plan The North American Numbering Plan ( NANP )

1533-412: The incumbent local exchange carriers for services, usually by forcing the existing sole service provider to lease infrastructure to other local providers. Because of the original design of the numbering plan and the telephone switching network that assumed only a single provider, number allocations had to be made in 10,000-number blocks even when many fewer numbers were required for each new vendor. Due to

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1606-541: The original North American area codes . The new numbering plan provided for 152 area codes, each with a capacity to serve as many as 540 central offices. Originally, only eighty-six area codes were assigned. New Jersey received the first NPA code in the new system, area code 201 . The second area code, 202 , was assigned to the District of Columbia . The allocation of area codes was readjusted as early as 1948 to account for inadequacies in some metropolitan areas. For example,

1679-644: The public switched telephone network (PSTN). The North American Numbering Plan conforms with International Telecommunication Union (ITU) Recommendation E.164 , which establishes an international numbering framework. From the Bell System's beginnings in 1876 and throughout the first part of the 20th century, telephone networks grew from essentially local or regional telephone systems. These systems expanded by increasing their subscriber bases, as well as increasing their service areas by implementing additional local exchanges that were interconnected with tie trunks . It

1752-401: The switchboard operator when a subscriber picked up the telephone handset to make a call. The operator answered requesting the destination of the call. When manual exchanges were replaced with automated switching systems, the exchange generated a tone to the caller when the telephone set was picked up, indicating that the system was ready to accept dialed digits. Each digit was transmitted as it

1825-512: The 1940s, the Bell System set out to unify the various existing numbering plans to provide a unified, systematic method for routing telephone calls across the nation and to provide efficient long-distance service that eventually did not require the involvement of switchboard operators. In October 1947, AT&T published a new nationwide numbering plan in coordination with the independent telephone operators. The plan divided most of North America into eighty-six numbering plan areas (NPAs). Each NPA

1898-602: The NANPA function was transferred to the IMS division of Lockheed Martin in Washington, D.C. In 1999, the contract was awarded to Neustar , a company created from Lockheed for this purpose. The contract was renewed in 2004, and again in 2012. On January 1, 2019, Somos assumed the NANPA function with a one-year bridge contract granted by the FCC with the goal of consolidating the NANPA function with

1971-558: The Pooling Administrator and identifying a long-term contractor. On December 1, 2020, Somos secured the $ 76 million contract for a term of eight years against one other bidder. The long-range vision of the architects of the North American Numbering Plan was a system by which telephone subscribers in the United States and Canada could themselves dial and establish a telephone call to any other subscriber without

2044-430: The United States have experienced rapid growth in the number of area codes, particularly between 1990 and 2005. The widespread adoption of fax , modem , and mobile phone communication, as well as the deregulation of local telecommunication services in the United States during the mid-1990s, increased the demand for telephone numbers. The Federal Communications Commission allowed telecommunication companies to compete with

2117-460: The United States, the standard "city" dial tone was a 600 Hz tone that was amplitude-modulated at 120 Hz. Some dial tones were simply adapted from 60 Hz AC line current. In the UK, the standard Post Office dialing tone was 33 Hz; it was generated by a motor-driven ringing machine in most exchanges and by a vibrating-reed generator in the smaller ones. Some later ringing machines also generated

2190-498: The area codes N10 were implemented for the Teletypewriter Exchange Service (TWX). It was already common practice for decades that the digits 0 and 1 could not appear in the first two digits of the central office codes, because the system of using the first two letters of familiar names for central offices did not assign letters to these digits. The digit 0 was used for operator assistance , and 1 , which

2263-485: The assistance of switchboard operators . While the dialing of telephone calls by subscribers was common-place in many cities across the continent for local destinations, long-distance telephone calls had to be patched through manually by telephone operators at typically multiple intermediate toll offices using a system known since 1929 as the General Toll Switching Plan . The immediate goal for improvement in

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2336-543: The change would have dialed 213-555-0123 and after the change 1-213-555-0123, which permitted the use of 213 as an exchange prefix in the San Jose area. The preceding 1 also ideally indicates a toll call ; however, this is inconsistent across the NANP because the FCC has left it to the U.S. state public utilities commissions to regulate for traditional landlines , and it has since become moot for mobile phones and digital VoIP services that offer nationwide calling without

2409-526: The cities of Los Angeles with area code 213 and New York with 212. This change also required modification of the local dialing procedures to distinguish local calls from long-distance calls with area codes. Requiring 1 to be dialed before the full number in some areas provided for area codes of the form N10 , such as 210 in the San Antonio , Texas, area and 410 in eastern Maryland . Therefore, someone calling from San Jose, California , to Los Angeles before

2482-504: The continent for direct-dialing of long-distance calls by customers, first possible in 1951 and expanded across the nation during the decades following. AT&T continued to administer the continental numbering plan and the technical infrastructure until the end of the Bell System , when administration was delegated to the North American Numbering Plan Administrator (NANPA), a service that has been procured from

2555-476: The convenience of the mobility is charged to the subscriber. Callers from outside the local-calling region of the assigned number, however, pay for a long-distance call, although domestic long-distance rates are generally lower than the rates in caller-pays systems. Conversely, an early advantage of caller-pays was the relative absence of telemarketing and nuisance calls to mobile numbers, although this advantage dwindled as robocallers found ways to reduce to zero

2628-478: The digits 2–9 , Y denotes any of the digits 0-8 , and X denotes any digit 0–9 . Using 0 or 1 as the first digit of an area code or central office code is invalid, as is a 9 as the middle digit of an area code; these are trunk prefixes or reserved for North American Numbering Plan expansion . Each three-digit area code has a capacity of 7,919,900 telephone numbers (7,918,900 in the United States). Despite

2701-429: The existing area code and the other areas receiving a new code. In an overlay, multiple codes are assigned to the same geographical area, obviating the need for renumbering of existing services. Subtle variations of these techniques have been used as well, such as dedicated overlays , in which the new code is reserved for a particular type of service, such as cellular phones and pagers, and concentrated overlays , in which

2774-460: The extra digit. In 1995, the North American Numbering Plan Administrator eliminated the requirement that the middle digit of an area code had to be either 0 or 1 , implementing fully interchangeable NPA and central office codes , that had already been anticipated since the 1960s, when interchangeable central office codes were sanctioned. The NANP numbering format may be summarized in the ten-digit notation NYX NXX-XXXX , where N denotes any of

2847-425: The first decade of the 21st century, most users selected bundle pricing plans that included an allotment of minutes expected to be used in the billing period, and most U.S. carriers since offer unlimited calling plans at mass-market prices. Industry observers have attributed the relatively low mobile phone penetration rate in the United States, compared to that of Europe, to the subscriber-pays model. In this model

2920-468: The first two digits of the central office code were still restricted to the range 2 to 9 , and the eight combinations that ended in 11 were reserved as special calling codes. This increased the numbering pool for central office codes to 640, and resulted in the partitioning of the prefix space ( 000 — 999 ). As the numbering plan grew during the 1960s using all-number calling, plan administrators at AT&T identified that by c.  1973 some of

2993-448: The form 5XX-NXX. As of January 2021, the codes 500, 521, 522, 533, 544, 566, 577, 588, 523, 524, 525, and 526 have been designated. These codes are used for fixed or mobile devices, and not assigned to rate centers. As addresses, they may or may not traverse the public switched telephone network (PSTN). Applications include the use as personal 500 numbers. Some carrier-specific services have used area code 700 . In Canada, area code 600

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3066-681: The goal was to enable local telephone companies to make as few changes as possible in their systems. The new numbering plan divided the North American continent into regional service areas, termed numbering plan areas ( NPA s). The divisions conformed primarily to the jurisdictional boundaries of the U.S. states and the Canadian provinces . Some states or provinces needed to be divided into multiple areas. NPAs were created in accordance with principles deemed to maximize customer understanding and minimize dialing effort, while reducing plant cost. Each NPA

3139-646: The island of St. Martin with the French Collectivity of Saint Martin which, like the rest of the French Caribbean, is not part of the NANP. The NANP is administered by the North American Numbering Plan Administrator (NANPA, formerly Administration ). This function is overseen by the Federal Communications Commission, which assumed the responsibility upon the end of the Bell System. The FCC solicits private sector contracts for

3212-431: The largest area codes in urban centers might run out of central office prefixes to install more individual access lines. For relief in these cases, they finally eliminated the requirement that the middle digit of the central office code could not be 0 or 1 . This resulted in the format of interchangeable central office codes , N X X , where N = 2–9 and X = 0–9 . The first cities that required this action, in 1974, were

3285-443: The marginal cost of each call placed. The integrated numbering plan also enables local number portability between fixed and wireless services within a region, allowing users to switch to mobile service while keeping their telephone number. The initial plan for area code overlays did allow for providing separate area codes for use by mobile devices, although these were still assigned to a specific geographical area, and were charged at

3358-462: The middle had to be divided (beginning with New Jersey's 201), but until 1995 all area codes assigned had none other than the digits 0 and 1 in this position. The eight codes of the form N11 ( N=2–9 ) were reserved as service codes . The easily recognizable codes of the form N00 were available in the numbering plan, but were not initially included in assignments. Additional area code patterns were later assigned for other services; for example,

3431-508: The most populous states to be divided into multiple NPAs, it was not the sole reason to subdivide a state. An important aspect was the existing infrastructure for call routing, which had developed during preceding decades, often independently of state boundaries. The rules of determining areas also attempted to avoid cutting across busy toll traffic routes, so that most toll traffic remained within an NPA, and outgoing traffic in one area would not be tributary to toll offices in an adjacent area. As

3504-515: The need for more area codes forced the NANPA to allow the digits 2 through 8 to be used as a middle digit in new area code assignments, with 9 being reserved as a last resort for potential future expansion. At the same time, local exchanges were allowed to use 1 or 0 as a middle digit. The first area codes without a 1 or 0 as the middle digit were area code 334 in Alabama and area code 360 in Washington, which both began service on January 15, 1995. This

3577-406: The need for non-geographic services by designating certain numbering blocks for such purposes. Many of these telephone numbers are selected from the easily recognizable codes (ERCs). System-wide toll-free calling, for which the receiving party is billed for the call, uses the number range with area codes of the form 8XX. Area code and central office prefixes for other non-geographic services have

3650-515: The new network design. The letter-to-digit translations were printed on the face of every rotary dial in the metropolitan areas, according to a scheme designed by W.G. Blauvelt in 1917, that had been used in the Bell System in large metropolitan areas since the early 1920s. The network reorganization standardized this system to using a two-letter, five-digit ( 2L-5N ) representation of telephone numbers in most exchanges in North America, or to using an equivalent all-numeric seven-digit numbering plans, as

3723-621: The private sector by the Federal Communications Commission (FCC) in the United States. Each participating country forms a regulatory authority that has plenary control of local numbering resources. The FCC also serves as the U.S. regulator. Canadian numbering decisions are made by the Canadian Numbering Administration Consortium . The NANP divides the territories of its members into numbering plan areas (NPAs) which are encoded numerically with

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3796-468: The proliferation of service providers in some numbering plan areas, many area codes were threatened with exhaustion of numbering resources. The number blocks of failed service providers often remained unused, as no regulatory mechanism existed to reclaim and reassign these numbers. Area codes are added by two principal methods, number plan area splits and overlays . Splits were implemented by dividing an area into two or more regions, one of which retained

3869-663: The purpose of call routing, but a nationwide system of participation in the NANP eventually failed. During the decades following, the NANP expanded to include all of the United States and its territories , Canada, Bermuda, and seventeen nations of the Caribbean. At the request of the British Colonial Office , the numbering plan was first expanded to Bermuda and the British West Indies because of their historic telecommunications administration through Canada as parts of

3942-405: The role of the administrator. Before the division of the Bell System, administration of the North American Numbering Plan was performed by AT&T's Central Services Organization. In 1984, this function was transferred to Bell Communications Research ( Bellcore ), a company created by the divestiture mandate to perform services for the newly created local exchange carriers . On January 19, 1998,

4015-488: The same rate as any other call. Consequently, the caller pays pricing model adopted in other countries, in which calls to cellular phones are charged at a higher nationwide rate, but incoming mobile calls are not charged to the mobile user, could not be implemented. Instead, North American cellular telephone subscribers are also generally charged for receiving calls ( subscriber pays ). In the past, this has discouraged mobile users from publishing mobile telephone numbers, but by

4088-543: The same rate as other area codes. Initially, the area code 917 for New York City was specifically assigned for this purpose within the boroughs; however, a Federal court ended the practice and the use of an area code for a specific telephony purpose. Since mobile telephony has been expanding faster than landline use, new area codes typically have a disproportionately large fraction of mobile and nomadic numbers, although landline and other services rapidly follow and local network portability can blur these distinctions. Canada and

4161-567: The system are the Dominican Republic and Puerto Rico . Mexican participation was planned, but implementation stopped after three area codes (706, 903 and 905) had been assigned, and Mexico opted for an international numbering format, using country code 52. The area codes in use were subsequently withdrawn in 1991. The Dutch Caribbean territory of Sint Maarten joined the NANP in September 2011, receiving area code 721 . Sint Maarten shares

4234-421: The system. The status of the network of the 1960s was represented by a new name used for technical documentation: North American Integrated Network . By 1975, the numbering plan was referred to as the North American Numbering Plan , resulting in the well-known initialism NANP , as other countries sought or considered joining the standardization. Although Bermuda and the Caribbean islands had been assigned

4307-486: The time President Dwight D. Eisenhower retired in 1961 it was nearly universal, but the president himself had never encountered a dial tone. When he picked up his own household phone, his assistant had to explain what the strange noise was, as well as show Eisenhower how to use a rotary dial phone. Before modern electronic telephone switching systems came into use, dial tones were usually generated by electromechanical devices such as motor-generators or vibrators . In

4380-481: The time of call establishment was to provide technology for the originating toll operators to dial calls directly to the destination. This system was known as Operator Toll Dialing . Operator Toll Dialing required a nationwide telephone numbering plan that unified all local numbering plans into a consistent universal system. Local numbering plans, many of which required only four or five digits to be dialed, or even fewer in small communities, needed to be expanded. but

4453-497: The title Dial Tone . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Dial_Tone_(disambiguation)&oldid=801909876 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Dial tone Early telephone exchanges signaled

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4526-429: The total number of digits in a subscriber telephone number to ten: a three-digit area code, three-digit central office code, and four digits for each line. This fixed format defined the North American Numbering Plan as a closed numbering plan , as opposed to developments in other countries where the number of digits was not fixed. In 1947, AT&T completed the new design for a nationwide toll network that established

4599-442: The usable leading digits of central office codes, imposed by using common names for central office names, and their leading two characters as guides for customer dialing could no longer be maintained when opening new central offices. By 1962 it was forecast that in 1985 the number of telephones in the nation would equal its population of 280 million and increase to 600 million telephones for 340 million people in 2000. As

4672-489: The widespread use of fictional telephone numbers of the form NYX 555-XXXX , only the block of line numbers from 0100 through 0199 are reserved specifically for this purpose, leaving the rest available for assignment. The country code for all countries participating with the NANP is 1 . The prefix digit 1 is also used within the NANP for long-distance dialing. NANP telephone numbers are usually rendered as NPA-NXX-XXXX or (NPA) NXX-XXXX . For example, 250 555 0199,

4745-403: Was also assigned a three-digit number unique within its NPA. The combination of NPA code and central office code served as a destination routing code for use by operators to reach any central office through the switching network. Due to the numerical structure of the numbering system, each NPA was technically limited to 540 central offices. Although the limitation to 540 central offices required

4818-512: Was assigned a unique three-digit code, typically termed NPA code or simply area code . These codes were first used in Operator Toll Dialing by long-distance operators in establishing calls via trunks between toll offices. The goal of automatic service required additional technical advances in the latest generation of toll-switching systems, completed by the early 1950s, and installation of new toll-switching systems in most numbering plan areas. The first customer-dialed direct call using an area code

4891-415: Was complete. The last of these, 610 , was assigned to Canada, but reassigned in 1992. These new area codes, as well as a few other codes used for routing calls to Mexico, were used for telephone area code splits during the late 1980s and early 1990s, as all other area codes using the original plan had been consumed. After the remaining valid area codes were used up by expansion, in 1995 the rapid increase in

4964-598: Was dialed which caused the switching system to select the desired destination circuit. Modern electronic telephones may store the digits as they are entered, and only switch off-hook to complete the dialing when the subscriber presses a button. Invented by engineer August Kruckow, the dial tone was first used in 1908 in Hildesheim , Germany. The Bell Telephone Manufacturing Company (BTMC) in Antwerp, Belgium, Western Electric 's international subsidiary, first introduced dial tone as

5037-421: Was identified by a unique three-digit code number, termed the numbering plan area code , which was prefixed to the local telephone number when calling from one NPA to another. Calling within the same numbering plan area did not require dialing the area code. The telephone exchanges —in the Bell System they were officially termed central offices —became local exchange points in the nationwide system. Each of them

5110-413: Was made on November 10, 1951, from Englewood, New Jersey , to Alameda, California . Direct distance dialing (DDD) was introduced subsequently across the country. By the early 1960s, DDD had become commonplace in cities and most towns in the United States and Canada. By 1967, the number of assigned area codes had increased to 129 as demand for numbers led to splits of some areas and other countries joined

5183-520: Was practiced by some telephone companies. The closed numbering plan did not require the subscriber to dial all digits. When making a local call or a call within the same numbering plan area, the area code was omitted in seven-digit dialing . In some cases, even fewer digits sufficed for local calling. Ten-digit dialing was only necessary when making foreign area calls to subscribers in another state or numbering plan area. Exceptions existed for communities on NPA boundaries, so that uniform local dialing

5256-422: Was still possible in historically established communities. All-number calling was a telephone numbering plan introduced in 1958, that converted telephone numbers with exchange names to a numeric representation of seven digits. The original plan of 1947 had been projected to be usable beyond the year 2000. However, by the late 1950s it became apparent that it would be outgrown by about 1975. The limitations for

5329-427: Was the responsibility of each local administration to devise telephone numbering plans that accommodated the local requirements and growth. As a result, the North American telephone service industry developed into an unorganized set of many differing local numbering systems. The diversity impeded the efficient operation and interconnection of exchanges into a nationwide system for long-distance telephone communication. By

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