Well, that didn't take long. Sprint today revealed that it has filed a suit against AT&T's proposed T-Mobile purchase -- and now AT&T is hitting back with some less than flattering words. An AT&T spokesperson told Engadget, "this simply demonstrates what we've said all along -- Sprint is more interested in protecting itself than it is in promoting competition that benefits consumers." AT&T went on to promise a "vigorous fight" and reiterated that such a merger would ultimately prove beneficial to the industry and consumers, improving wireless service and solving spectrum concerns.