Area code 313 was assigned as one of the original 86 area codes in October 1947, when it was designated to serve the southeastern quadrant of Michigan, including
Metro Detroit,
Flint, and the southern part of
The Thumb. The rest of the eastern half of the
Lower Peninsula was assigned to
area code 517. Because of the demand for new telephone service in Detroit's suburbs and neighboring areas, the northern portion, including Detroit's northern suburbs, Flint and the southern Thumb were split off with new
area code 810 on 1 December 1993 with a permissive dialing period that ended on August 10, 1994. On 13 December 1997, the remaining 313 area was reduced to its current size when the western portion, including
Ann Arbor,
Monroe County and western and
downriver Wayne County, received
area code 734 in another split. In February 2000,
area code 679 was reserved for future numbering relief in form of an
overlay complex for the 313 numbering plan area, as part of action for two other overlay plans in the larger Detroit metropolitan area. Opponents of the overlay relief plan cited the cultural importance and impact of area code 313, in which "313" is often synonymous with the city of Detroit. On March 17, 2025, the Michigan Public Service Commission announced an overlay complex with new area code 679 with an in-service of November 7, 2025, ==In popular culture==