My iPhone has been freezing up, restarting and quitting applications no matter what I do. It just started doing this about 2 weeks ago out of nowhere. I'm on T-Mobile, and I bought an iPhone through a friend who upgraded to 3G. The phone is still under warranty. If I restore the phone to it's original factory settings, and have a different friend use his AT&T SIM (who also has an iPhone) to take the phone to the Apple store to explain the situation.... will they know it's been unlocked? It's my experience that they don't do much investigation (i.e. they replaced my 80GB iPod Classic without questions). I need advice on how to get this fixed. I've restored, removed, and restarted... but no matter what... the problem persists. NOTHING, and I mean NOTHING is fixing this issue.