Alright, my friend has an iphone under contract with ATT. I have an unlocked/jailbroken iphone with a local provider. If I needed to go in for warranty work, after verginizing and everything, could my friend bring in my iphone and tell them that it was his second one that he uses as a backup with his iphone service from the first? If we were to put his sim in my phone would it activate the phone and allow it t work like his other one? Also would this cause problems for him when he put his sim back in his phone?