I just bought a used s6 from swappa and I am on tmobile but the phone is verizon based my understanding is its unlocked so should work I know my friends iPhone 6+ and nexus 6 worked fine on sprint and tmobile. I heard their will be issues with data and mms so would flashing a TMobile firmware fix these issues? Aren't all the phones the same? At&t/verizon/sprint/tmobile