No, I don't think you can. Check www.apple.com or www.att.com and try to find out!

YES, SURE! You only need to unlock and jailbreak your iPhone! The main tip is to avoid preety new ones, that you must to buy with service signature. Search for some used or new on e-bay or another place and follow some instructions on the web to unlock and jailbreak it. My iPhone is prepaid and I ensure that it is a good deal!

Best regards!