My cousin recently moved to the US from Austria. With him he brought an iPhone 3GS that runs on their T-Mobile network. My uncle gave him an AT&T sim card. How can I help him to it to work on his phone? He is running 4.1 software. Forgive my ignorance. I'm not an iPhone user, but I am somewhat Tech Savvy, and with some help, I'd like to save him from having to buy a new phone. Thanks in advance for your help.