Hello everyone, I am in need of a little advice. I have setup a deal to meet someone at an At&t store and he is going to purchase a new iphone 4 by cashing in his upgrade. He plans on keeping his 3GS and selling the iPhone 4 to me for a really good deal. Will I run into any issues setting up the phone? Will at&t send me a new microsim without any hassle? And will the phone still be under warranty once I have it in my possesion? Thanks in advance!