"It's a classic horizontal merger where they are taking a competitor out of the marketplace," Stephenson said. "Power to them if they get it done."
The comments are Stephenson's first on the deal since Sprint and T-Mobile announced a $26 billion merger last month. Stephenson spoke at the Code Conference in Rancho Palos Verdes, California on Wednesday.
Stephenson declined to take a position on whether or not the deal should get approved, arguing that his comments would get twisted because of AT&T's potential conflict of interest related to the deal's outcome.
"People will say, 'Well if he comes out and says he supports it, that means it must be anti-competitive because why would he want it? But if he comes out and says he's against it, that must mean it's pro competitive, so we ought to let it go,'" Stephenson said.
AT&T attempted to acquire T-Mobile in 2011 but backed down after the Department of Justice sued to block the deal. AT&T paid T-Mobile a breakup fee that Deutsche Telekom, which owns the majority of T-Mobile, valued at $6 billion in cash and wireless spectrum, when the deal failed.
Since then, cable companies have begun to enter the wireless market, including CNBC parent company Comcast. Stephenson acknowledged Sprint and T-Mobile are likely to get a different review from regulators than AT&T did because of the changing competition.