Credit: Engadget

AT&T announced today that starting tomorrow you'll be able to sign up and get unlimited mobile-to-mobile calling to any number regardless of carrier. This is likely another attempt to keep users on its network, but at least it's a good one. There are some limitations though. You have to manually sign up, be on an unlimited text messaging plan, and a qualifying Nation or FamilyTalk voice plan. Nobody actually knows what AT&T means by "qualifying" right now but we'll find out tomorrow. It's also unclear whether or not this will be an entirely new plan that includes messaging and unlimited mobile-to-mobile or just a free gift to unlimited messaging users. Probably the former.