I have an iPhone 3gs ver. 4.0 that was jailbroken with JailBreakMe.com and unlocked with UltraSn0w.
I authorized a prepaid SIM with T-Mobile and everything worked as expected.

AT&T is coming to my area (through the purchase of Alltel) and I would like to switch to a prepaid AT&T plan. I got an AT&T SIM card and set up an account. When I put in the AT&T SIM all I get is a 'no service'.

In reading some (many) forum entries, it was indicated that I need to 'hactivate' the iPhone to the AT&T SIM. The method suggested was to re-jailbreak but not re-unlock. I'm concerned about using JailBreakMe again as I don't know what will happen.

If I do use JailBreakMe with the AT&T SIM in the device will I be 'hactivated' and be able to use my new AT&T SIM card?

Any known problems?

Thank you in advanced for any help/insight you can give me.