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The system was based on fixed-length numbers; a direct-dial long-distance call consisted of a three-digit area code and a seven-digit local number. Numbers in 2L-4N cities (such as Montréal and Toronto ) were systematically lengthened to seven digits in the 1950s, a few exchanges at a time, so that all local numbers were seven digits when ...
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]
Area codes are also assigned for non-geographic purposes. The rules for numbering NPAs do not permit the digits 0 and 1 in the leading position. [1] Area codes with two identical trailing digits are easily recognizable codes (ERC). NPAs with 9 in the second position are reserved for future format expansion.
The differences between the prefixes are the length of the number (six or ten digits), the license cost to use them each year (approximately A$1 for 1800 and 1300, A$10,000 for 13 numbers) and the call cost model. 1300 numbers [8] and 13 numbers share call costs between the caller and call recipient, whereas the 1800 model offers a national ...
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 number may have ...
When dialing a telephone number, the area code may have to be preceded by a trunk prefix or national access code for domestic calls, and for international calls by the international access code and country code. Area codes are often quoted by including the national access code. For example, a number in London may be listed as 020 7946 0321.
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. For example, 234 235-5678 is a
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.