I'm trying to figure out whether I need to first activate my new iphone 4 with the At&T sim that will come with it (its a contract phone my brother is buying for me), or not? To be clear, its a phone he ordered on his AT&T line but he will give to me and continue to use his older phone. I use Tmobile, and am looking to unlock it. I understand the JB and unlock part and what I need to do, I just don't understand which is the best way to activate. Thanks in advance!