A state panel has approved a plan mandating 10-digit dialing for residents living in the 423 area code to make local phone calls.
The Tennessee Public Utility Commission earlier this week unanimously approved the move, which will affect callers within the sprawling area code that includes Chattanooga and most of the rest of East Tennessee except the Knoxville region.
John Hutton, telecom/utilities consultant for the commission, said Thursday that the changeover requiring the use of the 423 area code in front of a seven-digit telephone number likely will take about 13 months.
"There's a lot of work to be done," he said in a phone interview.
The reason for the move is because the telephone number pool within the area code is being exhausted, Hutton said.
"They don't ever want to get to the point where they run out of numbers, and we're not prepared," he said.
The availability of numbers within the 423 area code is dwindling because of growth in East Tennessee, he said.
Tim Schwarz, the commission's director of communication, said in a phone interview that after the shift is made to 10 digits, new telephone numbers issued to people in East Tennessee are likely to receive a newly created area code.
He said a similar change was made in Middle Tennessee nearly a decade ago, and the 629 area code was created for the new telephone numbers.
"It went pretty smooth," Schwarz said.
He said the other alternative considered by the commission was geographically splitting the 423 zone into two area codes.
But that would have required many people to have to change their existing phone numbers, Schwarz said.
"If we split the territory, it would have created a huge outcry when people change their numbers," he said. "People would be frustrated by that."
Schwarz said using a landline phone currently, callers within the area code already have to dial 423 for some calls deemed long distance within the zone.
The petition seeking the changeover for the 423 area code came from the North American Numbering Plan Administrator on behalf of the Tennessee telecommunications industry, according to the commission.
The group is a neutral third-party administrator of the numbering plans in North America. It said in its petition to the commission that the 423 area code is projected to exhaust its number pool in the third quarter of 2025.
Schwarz said there's an appeals process to the commission's recent action. Anyone can file a petition for reconsideration with the commission within 15 days of the panel's May 30 order. Or, there's the right of a judicial review in the Tennessee Court of Appeals, Middle Section, within 60 days.
Hutton said telecommunications providers will contact customers about the planned future change.
"All the providers will handle notification," he said.
Hutton said when the change was made in Middle Tennessee, some security companies experienced an issue. But since that time, he said, it's likely that those companies can more easily make the needed software changes.