A New Area Code Is Coming To Northeast Tennessee. The Tennessee Public Utilities Commission Has Approved The New 729 Area Code. Counties With The 423 Area Code Are Expected To Run Out Of New Numbers In The Third Quarter Of 2025. Existing Customers Will Keep Their Current Telephone Numbers But New Customers May Be Assigned The New 729 Area Code Once It Is Activated. No Date Has Been Set As To When The New Area Code Will Start.