In 1947, AT&T completed the new design for a nationwide toll network that established the original North American area codes. The new numbering plan provided for 152 area codes, each with a capacity to serve up to 540 central offices. [26] Originally, only eighty-six area codes were assigned. New Jersey received the first NPA code in the new system, area code 201. [27] 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, the Indiana numbering plan area 317 was divided to provide a larger numbering pool in the Indiana suburbs of Chicago ( area code 219).

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IDDD was implemented through extensive modifications in the switching systems to accommodate the international open numbering plan with seven to twelve digits in the national telephone numbers. [49] Access to the international network is facilitated by the dialing prefix 011, after which the country code and the national telephone number are dialed. 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 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 now offer nationwide calling without the extra digit. [ citation needed] Interchangeable NPA codes [ edit ] The telephone exchanges—in the Bell System they were officially called central offices—became local exchange points in the nationwide system. Each of them 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. [22] Due to the numerical structure of the numbering system, each NPA was technically limited to 540 central offices. [23] Covers Canada, the United States, parts of the Caribbean Sea, and some Atlantic and Pacific islands. The area code is often enclosed in parentheses. a b c Blair N.D., Cosgrove M.P. (AT&T), why all numbers?, Bell Telephone Magazine, Autumn 1962, p.10The Dutch Caribbean territory of Sint Maarten joined the NANP in September 2011, receiving area code 721. [13] Sint Maarten shares the island with the French Collectivity of Saint Martin which, like the rest of the French Caribbean, is not part of the NANP. Membership in the NANP brings significant advantages for countries in the vicinity of the United States and Canada, which usually are already the top dialing destinations. Both countries also originate most of the tourism business for the Caribbean. This is enhanced by the integration from sharing the same dialing procedures, without international access codes, and the toll-free number system of the NANP, as businesses in all member countries are eligible to participate. Call 658 ... Jamaica gets additional area code, 10-digit dialling becomes mandatory May 2018". 28 August 2017.

North American Numbering Plan - Wikipedia North American Numbering Plan - Wikipedia

The concepts underlying the NANP were originally devised in the 1940s by the American Telephone and Telegraph Company (AT&T) for the Bell System and the independent telephone companies in North America in Operator Toll Dialing. The first step was to unify the diverse local telephone numbering plans that had been established in the preceding decades, with the goal to speed call completion times and lower the costs for long-distance calling, by reducing manual labor by switchboard operators. Eventually, it prepared the continent for direct-dialing of long-distance calls by customers, first possible in 1951 and expanded across the nation in the decades following. AT&T continued to administer the continental numbering plan and the technical infrastructure until the breakup of the Bell System, when administration was delegated to the North American Numbering Plan Administrator (NANPA), a service that has been procured from the private sector by the Federal Communications Commission (FCC) in the United States. Each participating country forms a regulatory authority that has plenary control over local numbering resources. [1] The FCC also serves as the U.S. regulator. Canadian numbering decisions are made by the Canadian Numbering Administration Consortium. [2] Because of these higher fees, scams had taken advantage of customers' unfamiliarity with pricing structure to call the legacy regional area code 809. Some scams lured customers from the United States and Canada into placing expensive calls to the Caribbean, by representing area code 809 as a regular domestic, low-cost, or toll-free call. The split of 809 (which formerly served all of the Caribbean NANP points) into multiple new area codes created many new, unfamiliar prefixes which could be mistaken for U.S. or Canada domestic area codes but carried high tariffs. In various island nations, premium exchanges such as +1-876-HOT-, +1-876-WET- or +1-876-SEX- (where 876 is Jamaica) became a means to circumvent consumer-protection laws governing area code 900 or similar U.S.-domestic premium numbers. Rate Center Consolidations" (PDF). Archived from the original (PDF) on 2015-01-18 . Retrieved 2015-01-18. As the numbering plan grew in the 1960s under all-number calling, plan administrators at AT&T identified that by c. 1973 some of 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 removed 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 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. Under all-number calling, the number of permissible central office prefixes increased from 540 to potentially 800, but 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. [30] This increased the numbering pool for central office codes to 640, and resulted in the partitioning of the prefix space ( 000— 999). [32] Interchangeable central office codes [ edit ]Depending on the techniques used for area code and central office code relief, the effect on telephone users varies. In areas in which overlays were used, this generally avoids the need for converting telephone numbers, so existing directories, business records, letterheads, business cards, advertising, and "speed-dialing" settings can retain the same phone numbers, while the overlay is used for new number allocations. The primary impact on telephone users is the necessity of remembering and dialing ten-digit numbers when only seven-digit dialing was previously needed. Splitting numbering plan areas instead of overlaying generally avoids the requirement for mandatory area code dialing within the new regions, but at the expense of having to convert a region to the new code, which necessitates updating records and directories to accommodate the new numbers. A transition period prior to splitting provides a period of "permissive dialing" during which seven-digit dialing is still permitted. Also, many splits involved significant technical issues, considering municipal boundaries and tributary trunking arrangements. This section needs additional citations for verification. Please help improve this article by adding citations to reliable sourcesin this section. Unsourced material may be challenged and removed. ( February 2014) ( Learn how and when to remove this template message) ITU; ITU-T. "The International Public Telecommunication Numbering Plan". ITU . Retrieved 2015-07-25. FCC Designates 988 for the National Suicide Prevention Lifeline". Federal Communications Commission. 2020-07-16 . Retrieved 2021-12-06.