Area Code Atlas

NPA 313 assigned as original area code

Area code 313 was assigned in October 1947 as one of the original 86 area codes, serving the southeastern quadrant of Michigan, including Metro Detroit, Flint, and the southern Thumb.

NANP - INTERCHANGEABLE CENTRAL OFFICE CODES IN THE MICHIGAN 313 NPA

NANP-SPLIT OF 313 (MICHIGAN) NUMBERING PLAN AREA (NPA)

NPA 810 split from 313

Area code 810 was created in 1993 as a split from 313, taking over much of the territory outside of Monroe, Wayne, and Washtenaw counties in southeastern Michigan.

NPA 810 split from 313

Area code 810 was created on December 1, 1993, as a geographic split from area code 313. The new code covered east-central Michigan, including Flint, Lapeer, Port Huron, and surrounding counties, while 313 continued to serve Detroit and adjacent areas. A permissive dialing period followed the split.

Mandatory dialing for 810 and 313 after split

The permissive dialing period following the split of area code 313 ended on August 10, 1994. After this date, callers were required to use the correct area code—either 810 or 313—when dialing numbers in the affected regions.

End of permissive dialing between 313 and 810

The permissive dialing period ended on August 10, 1994, requiring callers to use the new area code 810 for numbers in the new numbering plan area, while 313 remained for the rest of southeastern Michigan.

NPA 734 split from 313

Area code 734 was created in 1997 as a geographic split from area code 313, serving southeast Michigan including Washtenaw and Monroe counties and parts of Wayne County.

NANP-Split of 313 (Michigan) Numbering Plan Area (NPA)

NPA 734 split from 313

Area code 734 was created in May 1997 by splitting from area code 313. The new code serves Washtenaw and Monroe counties and parts of Wayne County in southeast Michigan, including Ann Arbor and surrounding communities.

NPA 734 split from 313

On December 13, 1997, area code 734 was created in a split from 313. The western portion of the 313 area, including Ann Arbor, Monroe County, and western and downriver Wayne County, was assigned to 734.

NPA 679 reserved for future relief

In February 2000, area code 679 was reserved for future numbering relief as an overlay for the 313 area. The plan was part of a broader relief effort for the Detroit metropolitan area.

NPA 679 reserved for overlay relief of 313

Area code 679 was reserved in February 2000 as a future overlay code for the 313 numbering plan area to provide relief due to number exhaustion concerns.

Relief schedule for 679 canceled

In April 2000, the relief schedule for area code 679 was canceled and implementation of the overlay was suspended. Numbering conservation efforts delayed the need for immediate relief.

Suspension of Relief in the 248, 313 and 734 NPAs (Michigan)

Overlay relief with 679 suspended

Implementation of the 679 overlay relief plan was suspended in April 2000, delaying the introduction of the new area code for the 313 area.

313/679 overlay approved

The Michigan Public Service Commission approved an all-services distributed overlay for the 313 area code on May 18, 2023. The new 679 area code was designated to serve the same geographic area as 313, providing relief for number exhaustion.

NPA 679 overlay on 313 announced

NPA 679 to Overlay NPA 313 (Michigan)

Overlay complex with 679 announced

On March 17, 2025, the Michigan Public Service Commission announced the implementation of an all-services overlay complex for the 313 area code with new area code 679. The overlay was planned to address the exhaustion of available numbers in the 313 region.

Permissive ten-digit dialing begins for 313/679 overlay

A permissive dialing period for the 313/679 overlay began on April 7, 2025. During this period, callers could use either 7 or 10 digits for local calls within the affected area.

Mandatory 10-digit dialing for 313/679 overlay

Mandatory 10-digit dialing was implemented for the 313/679 overlay on October 7, 2025. After this date, all local calls within the area required the area code to be dialed. The permissive dialing period ended and seven-digit dialing was discontinued.

NPA 679 overlay in-service for Detroit

On November 7, 2025, area code 679 was activated as an overlay for the 313 numbering plan area. New telephone numbers in the Detroit region may be assigned the 679 area code, while existing 313 numbers remain unchanged.