Original North American area codes

The original North American area codes were established by the American Telephone & Telegraph Company (AT&T) in the immediate post-WWII period. The effort of creating a comprehensive and universal, continent-wide telephone numbering plan in North America had the eventual goal of direct distance dialing by telephone subscribers with a uniform destination addressing and call routing system for all public service telephone networks. The initial Nationwide Numbering Plan of 1947 established eighty-six numbering plan areas (NPAs) that principally followed existing U.S. state or Canadian provincial boundaries, but fifteen states and provinces were subdivided further. Forty NPAs were mapped to entire states or provinces. Each NPA was identified by a three digit area code used as a prefix to each local telephone number. The initial system of numbering plan areas and area codes was expanded rapidly in the following decades and established the North American Numbering Plan (NANP).

History

Early in the 20th century, the American and Canadian telephone industry had established criteria and circuits for sending telephone calls across the vast number of local telephone networks on the continent to permit users to call others in many remote places in both countries. By 1930, this resulted in the establishment of the General Toll Switching Plan, a systematic approach with technical specifications, for routing calls between two major classes of routing centers, Regional Centers and Primary Outlets, as well as thousands of minor interchange points and tributaries. Calls were manually forwarded between centers by long-distance operators who used the method of ringdown to command remote operators to accept calls on behalf of customers. This required long call set-up times with several intermediate operators involved. When placing a call, the originating party would typically have to hang up and be called back by an operator once the call was established.

The introduction of the first Western Electric No. 4 Crossbar Switching System in Philadelphia to commercial service, in August 1943, automated the process of forwarding telephone calls between switching centers. For the Bell System this was the first step to let their long-distance operators dial calls directly to potentially far-away telephones. While automatic switching decreased the connection times from up to fifteen minutes to approximately two minutes for calls between far-away locations, each intermediate operator still had to determine special routing codes unique to their location for each call. To make a nationwide dialing network a practical reality, and to prepare for eventual direct distance dialing (DDD) by subscribers, a uniform nationwide numbering plan was needed so that each telephone on the continent had a unique address that could be used independently from where a call originated. Such methodology is called destination routing.

With this goal, AT&T developed a new system called Nationwide Operator Toll Dialing during the 1940s. The effort proceeded with periodical communications to the general telecommunication industry via the Dial Interexchange Committee of the United States Independent Telephone Association. The planning came to a conclusion in October 1947, when results were presented to wider industry bodies. The new numbering plan became known as the nationwide numbering plan, and by 1975 it was known as the North American Numbering Plan, as efforts were in progress to expand the system beyond the United States and Canada.

Central office prefixes

Telephone dial number card of c.1948 with the local telephone number 4-5876 in Atlantic City, NJ, using the central office prefix 4, later converted to AT4

Building a nationwide network in which anyone can dial another telephone required a systematic numbering system that was easy to understand and communicate to the general public. Local telephone numbers varied greatly across the country, from two or three digits in small communities, to seven in the large cities. Based on the precedent and experience with the large-city dial systems in the nation, the designers set out to standardize every local telephone network in the nation to seven-digit local telephone numbers. This required no or only a few changes in the nation's largest cities. The large automatic dial switching systems were designed to provide service for up to ten thousand subscriber lines. Therefore, each telephone connected to such a switch had a four-digit line or station number.

Face of a 1939 rotary telephone dial with the telephone number LA-2697, which includes the first two letters of Lakewood, New Jersey, as the central office prefix, later converted to LA6

For calling a telephone connected to another switching system in the same city or in a nearby community, a routing prefix was used that was dialed before the line number. Central office prefixes had already been used in the cities' dial systems since the 1920s, and were typically dialed by subscribers as the initial letters of the exchange name, but only the largest of cities used three digits or letters. This practice and familiarity was preserved in the initial formulation of the new numbering plan, but was standardized to a format of using two letters and one digit in the prefix, resulting in the format 2L–5N (two letters and five numerals) for the subscriber telephone number.

This conversion required the addition of extra digits to the existing central office prefix. For example, the Atlantic City, New Jersey, telephone number 4-5876 was converted to AT4-5876 in the 1950s. Complete replacement of existing prefixes was necessary in the case of conflicts with another office in the state. Duplication of central office names or an identical mapping of two different names to digits was not uncommon. In practice, the conversion of the nation to this numbering plan took decades to accomplish and was not complete before the alphanumeric number format was abandoned in the 1960s in favor of all-number calling (ANC).

Numbering plan areas

Initial concepts for a nationwide numbering plan anticipated by 1945 to divide the continent into between fifty and seventy-five numbering plan areas. Considering this size of the network, a unique two-digit code for each numbering plan area (NPA) would have been sufficient. However, AT&T wanted to preserve existing dialing practices by only dialing the local number for local calls; it was therefore necessary to distinguish the NPA codes from central office codes. Central office codes could not have the digits 0 and 1 in the first two positions, because no letters were mapped to those to represent exchange names. This was the opportunity for distinction, but only when used in the second position, because switching systems already suppressed single loop interruption (corresponding to 1) automatically, and 0 was used to reach an operator or long-distance desk.

Therefore, numbering plan area codes, often called just area codes, were defined to have three digits, with the middle digit being 0 or 1. Area codes with the middle digit 0 were assigned to numbering plan areas that comprised an entire state or province, while jurisdictions with multiple plan areas received area codes having 1 as the second digit.

No codes of the forms N00, N10, and N11 (N is 2 through 9) occurred in the original area code allocation, leaving a total of 136 possible combinations. The series N00 was later used for non-geographic numbers, starting with intrastate toll-free 800 numbers in 1966. N10 numbers became teletypewriter exchanges, and N11 were used later for special services, such as information and emergency services.

The geographic layout of numbering plan areas across the North American continent was chosen primarily according to national, state, and territorial boundaries in Canada and the United States. While originally considered, no numbering plan area in the United States included more than a single state, but in Canada NPA 902 comprised all three territories of The Maritimes in the far east. The largest states, and some states with suitable call routing infrastructure were divided into smaller entities, resulting in fifteen states and provinces that were subdivided further, creating 46 NPAs. Forty NPAs were assigned to entire states or provinces.

The territories of the United States, which included Alaska, and Hawaii, did not receive area codes at first.

1947 division of the North American continent into 86 numbering plan areas

Initially, the area codes were used for nationwide Operator Toll Dialing by long-distance operators who dialed them for routing trunk calls between toll offices. This replaced the previous methods of ringdown forwarding between intermediate operators. Preparations proceeded for end-customer direct distance dialing (DDD) by establishing special automatic toll-switching centers based on new technology development for the No. 4 Crossbar Switching System, first installed in Philadelphia in 1943.

While the first customer-dialed call using an area code was made on November 10, 1951, from Englewood, New Jersey, to Alameda, California, it was not until the 1960s that direct distance dialing was common in most cities.

Area code assignment

The original configuration of the North American Numbering Plan assigned eighty-six area codes in October 1947, one each to every numbering plan area.

Area code	Country/State ID	State, province, or region
201	US:NJ	New Jersey
202	US:DC	District of Columbia
203	US:CT	Connecticut
204	CA:MB	Manitoba
205	US:AL	Alabama
206	US:WA	Washington
207	US:ME	Maine
208	US:ID	Idaho
212	US:NY	New York (New York City)
213	US:CA	California (Southern California, including Los Angeles)
214	US:TX	Texas (northeastern Texas, including Dallas/Fort Worth)
215	US:PA	Pennsylvania (southeastern Pennsylvania, including Philadelphia)
216	US:OH	Ohio (northeastern Ohio, including Cleveland)
217	US:IL	Illinois (central)
218	US:MN	Minnesota (except southeastern part of state)
301	US:MD	Maryland
302	US:DE	Delaware
303	US:CO	Colorado
304	US:WV	West Virginia
305	US:FL	Florida
306	CA:SK	Saskatchewan
307	US:WY	Wyoming
312	US:IL	Illinois (Chicago metropolitan area)
313	US:MI	Michigan (southeast Michigan, including Detroit)
314	US:MO	Missouri (eastern Missouri, including St. Louis)
315	US:NY	New York (central upstate New York, including Syracuse)
316	US:KS	Kansas (southern half of Kansas)
317	US:IN	Indiana (northern two-thirds of Indiana, including Indianapolis)
319	US:IA	Iowa (eastern third of Iowa)
401	US:RI	Rhode Island
402	US:NE	Nebraska
403	CA:AB	Alberta
404	US:GA	Georgia
405	US:OK	Oklahoma
406	US:MT	Montana
412	US:PA	Pennsylvania (western Pennsylvania, including Pittsburgh)
413	US:MA	Massachusetts (western Massachusetts, including Springfield)
414	US:WI	Wisconsin (southern and northeastern Wisconsin, including Milwaukee)
415	US:CA	California (northern/central California, including San Francisco and Sacramento)
416	CA:ON	Ontario (southern portion from Cobourg to Kitchener, including Toronto)
418	CA:QC	Quebec (eastern half of Quebec, including Québec City)
419	US:OH	Ohio (northwest Ohio, including Toledo)
501	US:AR	Arkansas
502	US:KY	Kentucky
503	US:OR	Oregon
504	US:LA	Louisiana
505	US:NM	New Mexico
512	US:TX	Texas (central and southern Texas, including Austin and San Antonio)
513	US:OH	Ohio (southwest Ohio, including Cincinnati)
514	CA:QC	Quebec (western half of Quebec, including Montreal)
515	US:IA	Iowa (central Iowa, including Des Moines)
517	US:MI	Michigan (south-central portion of Lower Peninsula, including Lansing)
518	US:NY	New York (northeastern New York, including Albany)
601	US:MS	Mississippi
602	US:AZ	Arizona
603	US:NH	New Hampshire
604	CA:BC	British Columbia
605	US:SD	South Dakota
612	US:MN	Minnesota (southeastern portion, including Minneapolis)
613	CA:ON	Ontario (all except a southern portion covering Oshawa-Toronto-Kitchener)
614	US:OH	Ohio (southeast, including Columbus)
616	US:MI	Michigan (Grand Rapids, Upper Peninsula, western portion of Lower Peninsula)
617	US:MA	Massachusetts (eastern Massachusetts, including Boston)
618	US:IL	Illinois (southern Illinois, including East St. Louis and Carbondale)
701	US:ND	North Dakota
702	US:NV	Nevada
703	US:VA	Virginia
704	US:NC	North Carolina
712	US:IA	Iowa (western third, including Sioux City)
713	US:TX	Texas (southeastern Texas, including Houston)
715	US:WI	Wisconsin (northern Wisconsin)
716	US:NY	New York (western New York, including Buffalo and Rochester)
717	US:PA	Pennsylvania (eastern half, except for the Delaware and Lehigh Valleys)
801	US:UT	Utah
802	US:VT	Vermont
803	US:SC	South Carolina
812	US:IN	Indiana (southern Indiana)
814	US:PA	Pennsylvania (northwestern and central Pennsylvania)
815	US:IL	Illinois (northern Illinois, except Chicago and Quad Cities)
816	US:MO	Missouri (northwestern Missouri, including Kansas City)
901	US:TN	Tennessee
902	CA:NS,PE,NB	Nova Scotia, Prince Edward Island, New Brunswick
913	US:KS	Kansas (northern half of Kansas)
914	US:NY	New York (southern New York, including Long Island, but excluding New York City)
915	US:TX	Texas (western Texas, including El Paso)
916	US:CA	California (northern California, but not including Sacramento)

Assignment plan

States with more than two NPAs
New York	212, 315, 518, 716, 914
Illinois	217, 312, 618, 815
Ohio	216, 419, 513, 614
Pennsylvania	215, 412, 717, 814
Texas	214, 512, 713, 915
California	213, 415, 916
Iowa	319, 515, 712
Michigan	313, 517, 616
States and provinces with two NPAs
Indiana, Kansas, Massachusetts, Minnesota, Missouri, Wisconsin, Ontario, Quebec

The number of central offices that could be effectively installed in a plan with two letters and one digit for the central office code was expected to be approximately 500, because acceptable names for central offices had to be selected carefully to avoid miscommunication. States that required this many offices had to be divided into multiple smaller areas. But size or population was not the sole criterion for division. A very important aspect was the existing infrastructure for call routing, which had developed in preceding decades independently of state boundaries. Since traffic between numbering plan areas would require special Class-4 toll switching systems, divisions attempted to avoid cutting busy toll traffic routes, so that most toll traffic remained within an area, and outgoing traffic from one area would not be tributary to toll offices in an adjacent area. On the other hand, it was already recognized in 1930 that too little granularity in the allocation pattern introduced expensive traffic back-haul requirements, conceivably resulting in congestion of the routes to the centers.

These considerations led to the configuration that was publicized in October 1947, which divided New York state into five areas, the most of any state. Illinois, Ohio, Pennsylvania, and Texas were assigned four area codes each, and California, Iowa, and Michigan received three. Eight states and provinces were split into two NPAs. The pattern of this official assignment of area codes is illustrated in the following tabulation, separated into U.S. states or Canadian provinces with a single area code, and those with multiple NPA assignments.

Single-NPA states and provinces
N	20N	30N	40N	50N	60N	70N	80N	90N
1	201 NJ	301 MD	401 RI	501 AR	601 MS	701 ND	801 UT	901 TN
2	202 DC	302 DE	402 NE	502 KY	602 AZ	702 NV	802 VT	902 NB NS PE
3	203 CT	303 CO	403 AB	503 OR	603 NH	703 VA	803 SC
4	204 MB	304 WV	404 GA	504 LA	604 BC	704 NC
5	205 AL	305 FL	405 OK	505 NM	605 SD
6	206 WA	306 SK	406 MT
7	207 ME	307 WY
8	208 ID
9
Multi-NPA states and provinces
N	21N	31N	41N	51N	61N	71N	81N	91N
2	212 NY	312 IL	412 PA	512 TX	612 MN	712 IA	812 IN
3	213 CA	313 MI	413 MA	513 OH	613 ON	713 TX		913 KS
4	214 TX	314 MO	414 WI	514 QC	614 OH		814 PA	914 NY
5	215 PA	315 NY	415 CA	515 IA		715 WI	815 IL	915 TX
6	216 OH	316 KS	416 ON		616 MI	716 NY	816 MO	916 CA
7	217 IL	317 IN		517 MI	617 MA	717 PA
8	218 MN		418 QC	518 NY	618 IL
9		319 IA	419 OH

In the group of multiple-NPA states, the area codes first assigned (upper left corner) may be identified with the toll switching locations of the Regional Centers established in the General Toll Switching Plan of 1929: New York City (212), Los Angeles (213), Dallas (214), Chicago (312), St. Louis (314), and San Francisco (415), supplemented by newer systems in Detroit (313), serving the busy toll route to Toronto, and in Philadelphia (215), which had been chosen for the first cut-over into commercial service of a No. 4 Crossbar toll switch in 1943. The remaining Regional Centers in Denver (303) and Atlanta (404) were located in states with just a single area code each.

Expansion

As the implementation of the new numbering plan commenced, and the planning and design of detailed routing infrastructure proceeded, several numbering plan areas were redrawn or added in following years, usually before any direct distance dialing was available to the public. In 1948, Indiana received an extra area code (219) for its Chicago suburbs in the west. In 1950, southwest Missouri received area code 417, which reduced the extent of the Kansas City numbering plan area and thus provided more prefixes in that population center. In 1951, the State of New York gained area code 516 on Long Island, and Southern California received area code 714, to reduce the numbering plan area of Los Angeles. After the successful initial trials of direct distance dialing in Englewood, NJ of late 1951, expansion of the numbering plan accelerated with four new codes in 1953, seven in 1954, and by the end of the decade thirty-one additional area codes had been created over the initial allotment of 1947. to satisfy the post-war surge in demand for telephone service. In 1960, AT&T engineers, while already estimating that the capacity of the numbering plan would be exceeded by 1975, prepared the nation for the next major step in the evolution of the network by eliminating central office names, and introducing all-number calling (ANC). ANC increased the number of central office prefixes possible in each numbering plan area from 540 to an eventual maximum of 792 after the introduction of interchangeable central office codes in the 1970s.

In popular culture

Numerous media outlets and blog-style online publication have commented on the history of the area codes. Such reports invariably state that area codes were assigned by a principle of counting pulses (clicks) of the rotary dial, which were minimized for the large metropolitan area, such as New York, Chicago, and Los Angeles, while assigning codes with many pulses to sparsely populated areas. However, no authoritative sources for this method are quoted, and none of the original Bell System documents support this. The concept appears to agree only for a few of the largest of cities, which were already designated Regional Centers for switching in the plan of 1929, and no correlation exists beyond those.

See also

• List of future North American area codes
• List of North American Numbering Plan area codes