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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 ...
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 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.
Worldwide distribution of country calling codes. Regions are coloured by first digit. Telephone country codes, but also sometimes referred to as "country dial-in codes", or historically "international subscriber dialing" (ISD) codes in the U.K., are telephone number dialing prefixes for reaching subscribers in foreign countries or areas via international telecommunication networks.
411 and 611 are commonly used in the United States, but not officially assigned by the Federal Communications Commission. The designation for special use in the NANP prevents their use as area codes and central office prefixes , eliminating about 8 million telephone numbers from assignment.
For example, 234 235-5678 is a valid telephone number; with area code 234, central office prefix (exchange) 235, and line number 5678. The number 234 911-5678 is invalid, because the central office code must not be in the form N11.
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.
There is an international format for recording a telephone number containing the country code, settlement code and telephone number, and the national format containing the settlement code and telephone number. To record Ukrainian telephone numbers, telephone codes for settlements do not have an initial zero, long-distance prefix: 0.