yes, a girl i work with did the exact same thing. She signed up with AT&T and got a free temp. phone until she can afford iPhone. Her contract with Sprint isn't up for a few weeks, so AT&T gave her a temporary # until her contract is up, then they will port her # over. I just hope she don't get her iPhone before me, i will be highly jealous haha. But definitely contact them first to be doubly sure. Some Cell companies will take any chance they get to charge you an early termination fee.