Located in the Eastern (GMT -05:00) time zone. Area code 313 serves the state of Michigan. This area code was assigned on January 1st, 1947. On January 1st, 1947 it went into service. 313 is a General Purpose Code. Dialing pattern for local calls within the same NPA (area code) is 7D. Area code 679 has been reserved as a future overlay to the 313 area.