Yea I ran into the same thing as t-moblie srvc is shotty here so I got the straighttalk att sim. Of course before this I activated srvc. with the sim that came with the tmo ver. F3 handset, which put a sim lock on the handset. It would likely work with the tmo straighttalk sim but for the att straighttalk sim you will likely have to purchase the handset unlock codes. I would suggest the code provider I used but not sure as this is really the place to advertise for commercial services.