AT&T Mobility will acquire 21,000 Corr Wireless subscribers and spectrum owned by the Alabama-based wireless carrier in a private transaction between Corr’s parent company C Spire Wireless and AT&T.

Corr was acquired by Mississippi-based C Spire (formerly Cellular South) in February 2010 as the carrier sought expansion into northeastern Alabama and western Georgia. But Corr’s network has never been upgraded beyond 2G service, and the Corr has traditionally positioned itself as a value priced feature phone provider. As its competitors have moved beyond 3G into 4G service and now pitch mostly smartphones, Corr has fallen behind.

Corr’s coverage area has not been a priority for larger carriers like Verizon Wireless and AT&T. The acquisition, which includes multiple PCS and 700MHz “C-Block” licenses, will bolster AT&T’s weak coverage in the region, which includes Huntsville, Oneonta, Decatur, Cullman, Hartselle, and Arab, Ala.

AT&T is expected to decommission much of Corr’s older equipment and replace it with 4G LTE service.

Customers may not have to immediately upgrade their phones. Corr Wireless, like AT&T, operates a GSM network.