Chosen Solution
I bough a iphone 6s locked on sprint can i unlock to use on at&t
Well, there is two ways to do this. You’d have to buy a board that is unlocked, then do a logic board replacement, or bring it to Apple, and they might be able to do this, not guaranteed though, speaking Apple. I have linked guides to do this below. You’ll have to find a logic board if you want to do it the first way. iPhone 6s Logic Board Replacement
