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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.
An area code overlay required additional technology in all affected switching systems to recognize the local area codes and select the appropriate routing for local calls, even within the wire center. This eliminated the possibility of maintaining seven-digit dialing, and required the dialing of ten digits for all calls.
The largest telephone numbering plan in North American is the North American Numbering Plan (NANP), serving 25 regions or countries. Other countries maintain an autonomous numbering plan with distinct country codes within the international E.164 specifications by the International Telecommunication Union.
This makes the fastest-dialing area code 212 (5 total clicks), followed by 312 and 213 (6 clicks). The area code 605 is much slower than these, at 21 clicks. Many large US cities generally had fast-dialing area codes with the middle digit 1. Touch-tone dialing, introduced later, eliminated the wait.
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.
Area code dialing is optional in most geographical area codes, except Moscow (area codes 495, 498, 499); it is mandatory for non-geographical area codes. E.123 international and Microsoft formats are used for writing local phone numbers as well; international prefix and country code 7 are replaced with trunk code 8 (or 8~CC ) when dialing a ...
A 9 would be inserted as the new second digit of all area codes (e.g. 212 would become 2912, 916 would become 9916). Permissive dialing would be allowed because exchange equipment, on detecting a 9 as the second digit of the area code, would respond appropriately to expect 11 digits, or 10 in the absence of a 9 in that position.
Washington, D.C. (area code 202) to adjacent areas of Maryland (area code 301) and Virginia (area code 703), discontinued on October 1, 1990, to allow assignment of a code in all three area codes. Hull from Ottawa (before 2006, as every Ottawa-Hull local number originally was reserved in both area code 613 and 819 ). [ 1 ]