Area code 423

As a result, the state's three area codes were roughly coextensive with the traditional Grand Divisions of Tennessee.

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.

[1] Relief planning discovered that the Tri-Cities had too much traffic to follow Knoxville into 865, but were not large enough for a new area code through a three-way split.

The Tennessee Regulatory Authority selected the first option, since overlays were a new concept at the time, and had encountered some resistance due to the need for ten-digit dialing.

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.