AT&T Inc. (T) said on Thursday that the head of its wireless unit, Stan Sigman, was retiring, and it appointed Ralph de la Vega as his successor.

De la Vega, previously group president of regional telecom and entertainment, was named president and CEO of AT&T Mobility, effective immediately. Sigman will assist with the transition through the end of the year, the company said.

De la Vega served as chief operating officer of the wireless unit from 2004 to 2006.