Ten-digit dialing

In the United States and Canada, 10-digit dialing is a popular term used to refer to the practice of including the area code of a phone number when dialing. Sometimes (see below), an initial "1" is used; such dialing is known as 11-digit dialing or national format.

"Standard" dialing

Traditionally, after the advent of area codes, the phone system allowed 7-digit dialing. Callers dial only the local portion of the phone number they wanted to reach, with the called number typically assumed to be in the same area code as that of the caller. For example, a person whose full national phone number was 212-555-7890 was able to call a number located at 212-555-3456 by simply dialing 555-3456.

In this case, it is only necessary to dial the area code for a domestic call when the area code of the called number was different from that of the calling number. Some communities on an area code boundary, such as Ottawa-Hull (613/819) or Washington, D.C. (202) implemented exchange code protection schemes to ensure the same seven-digit local number was not assigned in two different area codes in the same city; this allowed the entire community to remain a seven-digit local call. Code protection is not possible for calls across area code boundaries within split plan cities where area codes have been added due to a shortage of available local numbers; these local calls became ten digits when the code was split.