Area Code Atlas

NPA 423 split from 615

In 1995, area code 423 was created from the eastern portion of area code 615, including Knoxville, Chattanooga, and the Tri-Cities. This was the first new area code in Tennessee in 41 years and was implemented to address number exhaustion in East Tennessee.

NPA 423 split from 615

Area code 423 was created in September 1995 from a split of 615, assigning most of the eastern portion of 615—including Chattanooga, Knoxville, and the Tri-Cities—to the new code. The boundary largely followed the division between the Eastern and Central Time Zones.

Geographic Split of 423 (Tennessee) Numbering Plan Area (NPA); addition of 865 NPA

Permissive dialing period begins for 865 and 423

Permissive dialing began on October 1, 1999, allowing calls to Knoxville and the affected counties to be completed using either area code 423 or 865 during the transition period.

NPA 865 split from 423

Area code 865 was introduced for Knoxville and nine surrounding counties in East Tennessee on October 1, 1999, as a geographic split from area code 423. The split was implemented to address number exhaustion in the region, with 865 chosen to represent 'VOL' for the Tennessee Volunteers.

NPA 865 split from 423

On November 1, 1999, area code 865 was created for Knoxville and most of central East Tennessee, splitting from area code 423. The new code was chosen to correspond to 'VOL' for the University of Tennessee Volunteers. The split was implemented due to rapid number exhaustion in the region.

Permissive dialing period for 423 and 865

Permissive dialing of area code 423 continued across East Tennessee until April 22, 2000, allowing callers to use either 423 or the new 865 code during the transition period.

Mandatory dialing of area code 865

Mandatory dialing of area code 865 took effect on February 1, 2000, ending the permissive period and requiring all calls to Knoxville and the surrounding counties to use the new area code.

NPA 729 overlay approved for 423

On May 30, 2023, the Tennessee Public Utility Commission approved an all-services overlay of area code 423 with new area code 729. The overlay was implemented to address projected number exhaustion in the 423 region.

Overlay of 423 with 729 approved

The Tennessee Public Utility Commission approved an all-services overlay of area code 423 with new area code 729 on May 30, 2023, to address number exhaustion in eastern Tennessee.

NPA 729 overlay on 423 announced

NPA 729 to Overlay NPA 423 (Tennessee)

Permissive ten-digit dialing for 423/729 overlay begins

Permissive ten-digit dialing for the 423/729 overlay complex began on August 5, 2024, allowing calls to be completed using either seven or ten digits during the transition period to help customers adjust to the new overlay.

NPA 729 overlay on 423 announced

NPA 729 to Overlay 423 (Tennessee) – supersedes PL-619

Mandatory ten-digit dialing for 423/729 overlay

On August 5, 2025, mandatory ten-digit dialing will begin for all calls in the 423 and 729 area codes. After this date, all local calls must be dialed using the area code. The implementation is actual.

NPA 729 overlays 423

Area code 729 was activated as an overlay for area code 423 on September 5, 2025, allowing new telephone numbers in the same geographic region to be assigned the new code.