Significant events for area code 403
| Date |
Details |
| 1947 | The original area code for Alberta, the Yukon and the western area of the Northwest Territories |
| October 21, 1997 | Area codes 403 and 819 were split to create a new area code 867 to cover the Northwest Territories, the Yukon and Nunavet |
| January 25, 1999 | Area code 403 was split with 780 covering the northern and central areas of Alberta |
| September 20, 2008 | Area code 587 was overlaid on 403 and 780 |
| April 9, 2016 | Area code 825 was overlaid on the entire province. |
| January 21, 2022 | Area code 368 was overlaid on the entire province. |