Area code 403 is a telephone area code in the North American Numbering Plan (NANP) for the Canadian province of Alberta. The numbering plan area encompasses the southern third of the province, which includes 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 the original eighty-six area codes assigned by AT&T in 1947. Its numbering plan area (NPA) originally comprised the entire province of Alberta, the Yukon, and the western half of the Northwest Territories. It was the second-largest numbering plan area in the North American Numbering Plan and spanned more than one ninth of the circumference of the planet, from the 49th parallel north to the North Pole. On October 3, 1997, the numbering plan area was reduced to Alberta, and the Canadian territories were split off with the new area code 867.
Within only a year, 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. On January 25, 1999, the northern two thirds of Alberta, including Edmonton, was split from 403 and assigned the new area code 780. Generally, everything from Red Deer, Lacombe, and Ponoka southward stayed in 403. Permissive dialing of 403 continued across the province until May 18, 1999.
Within a decade, area code 403 was close to exhaustion once again. The projected exhaust date was March 2009.[1] The solution for mitigation was to implement area code 587 as a province-wide overlay for both numbering plan areas of the state.[2][3][4] Optional ten-digit dialing began on June 23, 2008 and became mandatory on September 12, 2008.[5] 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.[6]
On January 21, 2022, the province was once again overlaid with another area code, 368.[7][8]
The incumbent local exchange carrier (LEC) in 403 is Telus. Prior to 1997, the larger 403 included EdTel (Edmonton Telephones, now part of Telus) and Northwestel as incumbent LECs. Prior to 1990, Telus was known as Alberta Government Telephones and was a department of the provincial government.[9]
