I recently bought a first gen iPhone from a friend who got a 3G iPhone. I unlocked it and was going to start using it on T-Mobile. I installed some apps from the App Store and am having trouble with it freezing up often and needing to restart it. I asked the person I bought it from and she said it used to do that and she took it into Apple and they fixed the issue. The iPhone is still under warranty until Jan 15. What should I do? If I take it in as is I don't think they will cover it since its unlocked. Should I put the legit sim card in it from my friends 3G iPhone and then take it in? Would I want to reset the phone before then? Like I said its unlocked but not Jailbroken. Any advice would be much appreciated.