Hello All! I am trying to research how I will be able to use an AT&T iPhone 5 on T-Mobile. This is what I am understanding so far: I will need to buy a iPhone from an Apple store full price and there is a way on iTunes to unlock the AT&T iphone? (By clicking restore?). Now I am reading that I will need an AT&T sim card to activate the phone first. Can someone please walk me step by step on how I would be able to successfully use an iPhone 5 on T-Mobile?