Detroit-area phone users must adjust to new dialing rules as a new 679 overlay area code is introduced.

10-Digit Dialing to Become Mandatory in Detroit’s 313 Area Code

Residents and businesses in Detroit and its surrounding suburbs will soon be required to dial 10 digits for all local calls as Michigan prepares to introduce a new 679 overlay area code for the 313 region.

With available phone numbers in the 313 area code running out, the Michigan Public Service Commission (MPSC) has announced that a new 679 area code will begin serving the same geographic area on November 7, 2025. As a result, phone users will need to include their area code when making local calls.

Key Dates: Transition to 10-Digit Dialing

To help residents and businesses adjust, a six-month permissive dialing period will begin on April 7, 2025. During this time, calls within the 313 area code can be placed using either seven or 10 digits. However, starting on October 7, 2025, seven-digit calls will no longer go through, and callers will hear a message instructing them to hang up and dial again using the full 10-digit number.

Beginning November 7, 2025, new phone numbers assigned in the area may have the 679 area code. However, current 313 numbers will not change, meaning existing customers can keep their current phone numbers.

What Detroit-Area Residents and Businesses Need to Know

Your phone number will not change. Existing 313 numbers remain active.
You must dial the full 10-digit number for local calls.
Long-distance calls will still require dialing 1 plus the area code and phone number.
Call pricing and service areas will not change.
Emergency services will still be accessible by dialing 911, 988, and other three-digit numbers such as 211, 311, 511, and 811.

Businesses and residents should update automatic dialing equipment, call-forwarding settings, speed dial lists, and alarm/security systems to accommodate the new dialing format before the October 7 deadline.

Updating Devices and Services to Avoid Disruptions

The transition to 10-digit dialing means phone customers must ensure that all communication devices recognize and support the new system. Affected services may include:

Medical alert devices and security systems
Fax machines and Internet dial-up services
Call forwarding and voicemail settings
Business marketing materials and stationery
Pet ID tags and personal contact lists

Customers with older home security or medical alert systems should contact their service providers to ensure compatibility with 10-digit dialing. The transition period from April 7 to October 7, 2025, provides time to make these adjustments.

Why Is a New Area Code Needed?

The 313 area code, originally established in 1947, has been shrinking due to increasing demand for phone numbers from mobile devices, businesses, and services. The MPSC projects that the 313 area code will be exhausted by late 2027, at which point new customers will receive numbers in the 679 area code.

While overlays like this preserve existing phone numbers, they require adjustments to dialing habits. Similar transitions have occurred in other parts of Michigan, including Grand Rapids and the Lansing area, where overlay area codes have been implemented.

Stay Informed and Prepared

For additional details on the transition and steps to prepare, visit the Michigan Public Service Commission’s website at www.michigan.gov/mpsc/consumer/telecommunications/numbering.

For questions about personal or business phone services, contact your local telephone provider or call MPSC’s Customer Assistance at 800-292-9555.

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