Mr. Sievert, 32, who will oversee all marketing and advertising activities for the company, steps into the newly created position from E-Trade Group, where he was the chief marketing and sales officer.
He is charged with creating an overall marketing and brand strategy for the company that extends to voice and data services.
The campaign, created by WPP Group's Ogilvy & Mather Worldwide, New York, has received mixed reviews.
There also are ongoing discussions with Metropolitan Life Insurance Co., or Met Life, about AT&T's use of mLife as a theme and slogan.
The insurance and financial services giant withdrew its allegation of trademark infringement, but a Met Life spokeswoman said discussions continue about the root issues of the squabble.
A spokesman for AT&T Wireless had no comment on the issues surrounding the situation but confirmed that both sides are continuing to talk.