Randall Stephenson, former chief operating officer of AT&T Inc., takes the reins today as CEO at AT&T.

San Antonio ? After an acquisition binge that transformed the smallest Baby Bell into a telecommunications heavyweight, AT&T Inc. is undergoing another change today: a new chief executive.

Randall Stephenson, 47, rose through the ranks of AT&T and previously served as its chief financial officer and chief operating officer. He is credited with helping position the company so it could afford the buying spree that turned it into the nation’s largest provider of traditional phone, wireless and broadband services.

Stephenson takes over for Edward Whitacre Jr. in time for what might be the most hyped telecommunications device launch in a generation, Apple Inc.’s iPhone. AT&T – whose wireless division was formerly known as Cingular – will be the exclusive carrier for the combination cell phone, portable music player and Web device when it launches in the U.S. later this month.

“Whatever your expectations are from this device, they are probably too low,” Stephenson said in a recent interview. “It changes how we think about the PDA (personal digital assistant), the iPod and the cell phone interacting.”

More than 1 million people have signed up through AT&T’s Web site for a call when the iPhone becomes available, Stephenson said. It will be available in two models, priced at $499 or $599.

It’s not clear how many of the devices will be available at launch, but Stephenson said, “I’ll be really disappointed if there’s not a shortage.”

AT&T plans to grow through wireless, using that business segment to drive sales of its traditional phone, high-speed Internet and other services.

“The company is going to be positioned as a wireless-centered company,” Stephenson said. “Once you have mom and dad and the kids on wireless, then you get them on broadband and television.”

He said he doesn’t plan major departures from the path San Antonio-based AT&T is following, after takeovers of BellSouth Corp., the Cingular Wireless business and the AT&T long-distance business. The BellSouth acquisition gave it full control of Cingular.

Most of the major consolidation in the telecommunications business is done, he said.

“No hard left or right turns. We’ve set the direction of this business over the last two to three years,” he said.

AT&T’s stock has been trading at five-year highs.