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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.
Each three-digit area code has a capacity of 7,919,900 telephone numbers (7,918,900 in the United States). Despite 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 prefixes in the Americas start with one of 1,2,5. All countries in the Americas use codes that start with "5", with the exception of the countries of the North American Numbering Plan, such as Canada and the United States, which use country code 1, and Greenland and Aruba with country codes starting with the digit "2", which mostly is used by countries in Africa.
For example, a telephone number in North America consists of a three-digit area code, a three-digit central office code, and four digits for the line number. If the numbering plan area does not use an overlay plan with multiple area codes, or if the provider allows it for other technical reasons, seven-digit dialing may be permissible for calls ...
United States telephone numbers often included letter prefixes and telephone exchange names, which were more easily memorable for users than long digit sequences. Subscriber number The subscriber number is the address assigned to a telephone line or wireless communication channel terminating at the customer equipment.
This was accomplished by adding the digit "9" to the beginning of any phone number that started with a "9" (government and semi-government connections), and adding the digit "3" to any phone numbers that did not start with the number "9". [1] It is common to write phone numbers as (0xx) yyyyyyy, where xx is the area code.
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]
The expansion of the North American Numbering Plan (NANP) is the anticipated requirement for providing more telephone numbers to accommodate future needs beyond the pool of ten-digit telephone numbers. Ten-digit telephone numbers have been in use in the United States and Canada in long-distance telephone service since the 1950s.