Area code 403 is a telephone area code in the North American Numbering Plan (NANP) for the southern third of the Canadian province of Alberta, including the Calgary area. This numbering plan area is also served by area codes 587, 825, and 368, which form a complex overlay for all of Alberta.
Area code 403 was one of nine Canadian area codes of the original North American area codes assigned by the American Telephone and Telegraph Company (AT&T) in 1947. Its numbering plan area (NPA) originally comprised the entire province of Alberta. During the course of the expansion of telephone service in the Northwest Territories and Yukon, these were serviced primarily with the same area code starting in 1960. [1] [2] For much of this time, 403 was geographically one of the largest NPAs in North America. On October 21, 1997, area code 867 was formed out of the territories' portion of 403 and the portion of area code 819 located in the Northwest Territories.
By early 1997, area code 403 was threatened by exhaustion because of the rapid growth of telecommunication services demand for pagers, cellphones, and computer modems, as well as growing competition among providers. [3] By September of 1997, Telus Communications and the Canadian Radio and Television Commission initiated relief actions in planning a north/south split of the 403 numbering plan area, with a boundary line drawn north of Red Deer and Stettler. The split became effective on January 25, 1999, so that the northern part, including Edmonton, received the new area code 780. [4] Permissive dialing of 403 for calls terminating in the new 780 numbering plan area continued across the province until July 12, 1999.
Within a decade, area code 403 was close to exhaustion once again. The projected exhaust date was March 2009. [5] The solution for mitigation was to implement area code 587 as a province-wide overlay for both numbering plan areas of the province. [6] [7] [8] Optional ten-digit dialing began on June 23, 2008 and became mandatory on September 12, 2008. [9] On September 20, 2008, Telus Mobility began to assign 587 telephone numbers to new customers in Calgary and Edmonton.
On April 9, 2016, all three numbering plan areas of the province were overlaid with an additional area code, 825. [10]
On January 21, 2022, the province was once again overlaid with another area code, 368. [11] [12]
The incumbent local exchange carrier (ILEC) in 403 is Telus. Prior to 1997, the larger 403 included EdTel (Edmonton Telephones, now part of Telus) and Northwestel as ILECs. Before 1990, Telus was known as Alberta Government Telephones and was a provincial government department. [13]
| North: 780/368/587/825 | ||
| West: 250/778/236/672 | 403/368/587/825 | East: 306/639 |
| South: 406 | ||
| British Columbia area codes: 250, 604, 236/257/672/778 | ||
| Saskatchewan area codes: 306/639/474 | ||
| Montana area codes: 406 | ||