KNOXVILLE, TN ( Story courtesy of WVLT) -With a new area code coming to East Tennessee in September, 10-digit dialing will be required beginning next week.

The Tennessee Public Utility Commission announced on Tuesday that starting on Aug. 5, all local calls made within the 423 area code must be dialed using 10 digits, which is the area code and the seven-digit telephone number.

After Aug. 5, calls only using seven digits won’t be completed and will be routed to an announcement.

This is all in preparation for the introduction of the new 729 area code, which officially begins rolling out on Sept. 5. This area code will coexist everywhere in the 423 region.

Officials said starting Sept. 5, new telephone lines or services may be assigned this new area code. Anyone receiving a 729 number will also be required to dial all 10 digits.

Current telephone numbers, including your current area code, will not change, officials said. Additionally, you can still dial just three digits to reach 911, 988 and 211, 311, 411, 511, 611, 711 and 811 where available.

The commission said you can do the following to prepare for the new dialing procedure:

• Identify your telephone number as a 10-digit number and include the area code when giving the number to friends, family, business associates and customers, etc.
• Ensure all services, automatic dialing equipment, or other types of equipment that are programmed to dial a 7-digit number are reprogrammed to include the area code and to recognize the new 729 area code as a valid area code.
• Update websites, personal and business stationery and checks, advertising materials, personal and pet ID tags, and other such items to ensure the area code is included.

This comes after 10-digit dialing became mandatory for the 865 area code in October 2021.

Original TN Government release:

Mandatory 10-Digit Dialing Is Coming to the Tennessee 423 Area Code Effective August 5, 2025

Wednesday, February 05, 2025 | 12:00am

To ensure new telephone numbers are available, the Tennessee Public Utility Commission approved the addition of the new 729 area code to the geographic region served by the 423 area code. This process is known as an area code overlay.

What is an area code over overlay?

An overlay is the addition of another area code (729) to the same geographic region as an existing area code (423). An overlay does not require customers to change their existing are code, but does require using a new 10-digit dialing procedure to complete local calls.

Who will be affected?

Anyone with a 423 area code will be affected. The 423 area code covers two non-contiguous regions in Eastern Tennessee, serving communities such as Chattanooga, Bristol, Johnson City and Kingsport, as well as many other smaller communities. The new 729 area code will serve the same geographic region currently served by the existing 423 area code.

What is the new 10-digit dialing procedure?

All local calls within  the 423 area code that are currently dialed with 7 digits will need to be dialed using 10 digits (area code + 7-digit telephone number). The same dialing procedure will apply to telephone numbers that are assigned in the new 729 area code.

When will the dialing change begin?

Effective August 5, 2025, you must dial 10 digits (area code + 7-digit telephone number) on all local calls including calls within your same area code. On and after this date, if you dial just 7 digits your call will not be completed, and a recording will instruct you to hang up and dial again, including the area code.

Beginning September 5, 2025, new telephone lines or services may be assigned numbers with the new 729 area code. If you have a number in the new 729 area code, you must dial 10 digits or the call will not complete.

What will you need to do to prepare:

• Dial 10 digits (area code + 7-digit telephone number) for local calls.
• All services, automatic dialing equipment, or other types of equipment that are programmed to dial a 7-digit local number must be reprogrammed to include the area code no later than August 5, 2025. Some examples include: life safety systems and medical monitoring devices, fire or burglar alarm and security systems or gates, fax machines, Internet dial-up numbers, contact lists in wireless or mobile phones, speed dialers, call forwarding settings, voicemail services and similar functions, etc.
• Update your websites, personal and business stationery and checks, advertising materials, personal and pet ID tags, and other such items to ensure the area code is included.

What will remain the same:

• Your telephone number including current area code.
• The price of a call, coverage area, or other rates and services will not change due to the overlay.
• What is a local now will remain a local call regardless of the number of digits dialed. 
• You can still dial just three digits to reach 911 and 988, as well as 211, 311, 411, 511, 611, 711 or 811 if available in your area.