Area code 423
Principal cities in the northern part of the area code region are Bristol, Johnson City, and Kingsport (more commonly known as the Tri-Cities). The principal cities in the south are Chattanooga and Cleveland.
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. 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 early 1999, 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 was decided to split off the Knoxville area as area code 865. The split began in October 1999 and became mandatory in February 2000.
This created one of the few area codes in the nation that is not contiguous, as 865 is almost entirely surrounded by 423. While neither Chattanooga nor the Tri-Cities were large enough for their own area code, they were too large to follow Knoxville into 865. 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. 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 2015.
- See Brewer, Bill. "423 Area Code To Become VOL In 9 ET Counties." Knoxville News-Sentinel. April 17, 1999.
- Tennessee Regulatory Authority press release, April 29, 1999