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.
You will not be able to change back but you will be able to use your phone with any carrier's sim card from now on. Including AT&T if you want to.