I'm trying to see if anything can be done in this situation. I had an iPhone sold to me and I gave it to my sister. I probably should have known but I bought it from some guy. Turns out it was an att iPhone. My sister had been using it for almost 3 months now on T-Mobile. It suddenly had no signal. She called and they said it has been locked. She called att and asked what could be done. That the owner of the phone would have to be contacted. Not sure if they do that or not. But is there a way around this? Curious.