Area code 423

Area code 423 was created in 1995 when it was split off from area code 615. It was the state's first new area code in 41 years. Originally, it consisted of the eastern third of the state, including Knoxville, Chattanooga and the Tri-Cities. The boundary between 423 and 615 roughly followed the line between the Eastern and Central time zones; generally, Tennessee's share of the Eastern Time Zone was in 423. As a result, the state's three area codes were roughly coextensive with the traditional Grand Divisions of Tennessee; 423 served almost all of East Tennessee, 615 served Middle Tennessee, and 901 served West Tennessee.

The Tennessee Regulatory Authority intended this configuration to be a long-term solution. However, by the mid-1990s, 423 was already close to exhaustion due to the proliferation of cell phones and pagers. The supply of numbers was further limited because the Tri-Cities area is part of a LATA that spills into Virginia, while the Chattanooga LATA spills into Georgia. As a result, several numbers in Virginia's 540 (now in 276) and Georgia's 706 weren't available for use. It soon became apparent that East Tennessee needed another area code, even though this would have forced many residents and businesses to change their numbers for the second time in a decade.

It was decided to split off the Knoxville area as area code 865. Normal practice would have called for Knoxville to retain 423, as it was the largest city in the old 423 territory. However, the Tennessee Regulatory Authority asked for Knoxville to receive 865 because on a standard telephone keypad, those numbers correspond to "VOL"--shorthand for "Volunteers," the nickname for the sports teams at the University of Tennessee.[1][2]

When plans were drawn up for the split, it was discovered that the Tri-Cities were too large to follow Knoxville into 865, but not large enough for their own area code. This left the Tennessee Regulatory Authority with two options–turn 865 into an overlay for all of East Tennessee, or make two non-contiguous sections of 423. Overlays were a new concept at the time, and met with some resistance due to the need for ten-digit dialing. The Regulatory Authority chose the second option.

865 began its split on October 1, 1999; permissive dialing of 423 continued across East Tennessee until February 1, 2000.[1][2] This created one of the few area codes in the nation that is not contiguous, as 865 is almost entirely surrounded by 423 and the North Carolina border. Although this seemed to be a temporary solution, the North American Numbering Plan Administration initially determined that the reconfigured 423 would not be exhausted until around 2010.[3] However, with the 2002 implementation of number pooling in the southern portion of the area code (the Chattanooga area), the Tennessee Regulatory Authority now projects that 423 will remain in its unusual, non-contiguous state until at least 2027.[4]

• NANPA area code map of Tennessee
• List of exchanges from AreaCodeDownload.com, 423 Area Code