I have an att connection with a 15$ data plan which is for 3g data access on non smart phones. Can I buy an iphone 3g on craigslist, put the att sim on this phone and use the same data plan? If not, If I jailbreak the phone would i be able to use on the same data plan? Would att automatically change my data plan to 30$ plan? Pls throw some light. Also, once a phone is jailbroken and its updated to new version of OS say 3.0.2, does it need to be jailbroken again? how much does it cost to jailbreak? your inputs are greatly appreciated.