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] until the territories received area code 867 on October 21, 1997.
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 in the new numbering plan area continued across the province until July 12, 1999, for calls terminating in the new numbering plan area.
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]
