Hi there, I have no knowledge about iphones so excuse my ignorance on the subject. My old man has offered me an iPhone 4, I'm not sure what.network it is on, I think it is o2, now being the idiot he is being crap with his money, he has not paid the bill and the phone has now been barred from outgoing calls, he has offered it to me for free if I can obviously unlock it, now would I be able to just put a new sim in it or is it a bit more complicated than that? I have a contract with t.mobile so ideally I would like to put my sim into this phone, would that be possible?