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Telephone numbers listed in 1920 in New York City having three-letter exchange prefixes. In the United States, the most-populous cities, such as New York City, Philadelphia, Boston, and Chicago, initially implemented dial service with telephone numbers consisting of three letters and four digits (3L-4N) according to a system developed by W. G. Blauvelt of AT&T in 1917. [1]
A telephone keypad using the ITU E.161 standard. A telephone keypad is a keypad installed on a push-button telephone or similar telecommunication device for dialing a telephone number. It was standardized when the dual-tone multi-frequency signaling (DTMF) system was developed in the Bell System in the United States in the 1960s – this ...
Telephone prefix. A telephone prefix is the first set of digits after the country, and area codes of a telephone number. In the North American Numbering Plan countries (country code 1), it is the first three digits of a seven-digit local phone number, the second three digits of the 3-3-4 scheme. In other countries, both the prefix and the ...
Zone 5 uses eight 2-digit codes (51–58) and two sets of 3-digit codes (50x, 59x) to serve South and Central America. Zone 6 uses seven 2-digit codes (60–66) and three sets of 3-digit codes (67x–69x) to serve Southeast Asia and Oceania. Zone 7 uses an integrated numbering plan; two digits (7x) determine the area served: Russia or Kazakhstan.
All-number calling. All-number calling (ANC) is a telephone numbering plan that was introduced into the North American Numbering Plan by the Bell System in the United States starting in 1958 [1] to replace the previous system of using a telephone exchange name as the first part of a telephone number. [2] The plan prescribed the format of a ...
The North American Numbering Plan (NANP) divides the territories of its members into geographic numbering plan areas (NPAs). Each NPA is identified by one or more numbering plan area codes (NPA codes, or area codes), consisting of three digits that are prefixed to each local telephone number having seven digits.
The national telephone numbering plan is maintained by Ofcom, an independent regulator and competition authority for the UK communications industries. This list is based on the official standard, but includes defunct codes and historical changes, including the derivation of the two letter identities, in cases where known.
A vertical service code (VSC) is a sequence of digits and the signals star (*) and pound/hash (#) dialed on a telephone keypad or rotary dial to access certain telephone service features. [1] Some vertical service codes require dialing of a telephone number after the code sequence. On a touch tone telephone, the codes are usually initiated with ...