for the 5s and now the 6 the ATT, T-mobile, Verizon are all the same model. They all have the same hardware, the difference is that the "GSM" model as they call it just have the CDMA portion of the radio chip disabled from the factory. Why? I have no idea, so thats why the Verizon model which is permanently factory unlocked is the best one to have because it can be used with everyone with the exception of Sprint. I always buy the Verizon version because resale is much better when the time comes.