BARCELONA—AT&T Inc. said it is considering a way to let the providers of mobile services pay for the cost of the data traffic associated with things like streaming movies and smartphone applications, opening up a new round of debate over the rules of the mobile Internet.

John Donovan, the executive responsible for AT&T's network and technology, explained the carrier's interest in the service in an interview, likening it to toll-free calling for the mobile-broadband world.

"A...