Ok i have a iphone 3gs(AT&T) with baseband 05.16.02. Ultrasn0w only works with basebands, 04.26.08, 05.11.07, 05.12.01, 05.13.04, and 06.15.00. Ultrasn0w allows you to use other carriers other than AT&T. Ok so when im about to jailbreak and unlock my phone it askes me if i want to change to the ipad 06.15.00 baseband. And that if i do change to 06.15.00 i will not be able to change back. So if i do change my phone to the ipad 06.15.00 will i be able to use the phone service with other carriers sims card. And never again AT&T. Thanks for you help in advance.