Hello! I have my att GSM iphone 7, model a1778, recently paid off and unlocked by my carrier att. My friend would like to use it on her metro pcs account, but her sim showed no service. We researched but have not found a definite answer. I see the phone is a GSM version, I had thought metro was CDMA, but I saw some articles online showing the phone should work. Is it possible to use the phone on metro, and how would I make that work? Thanks for your help!