It seems that Apple's Firmware Update to the iPhone cause the reactivation with AT&T. Sorry folks seems like Apple doesn't like anyone tampering with their equipment.
If you haven't already bitten the bullet and taken your unlocked iPhone down that scariest of paths, the 1.1.1 update, we're here to sort out a bit of the hearsay from the actual and fairly inconvenient truth. Even if you have already updated, or never even unlocked or jailbroke your iPhone to begin with, there's still a lot to learn, so let's dive in, shall we?
Most people with a jailbroken iPhone will end up with a "factory-fresh" iPhone after the 1.1.1 firmware update. Your mileage may vary, and isolated incidents of bricking have occurred, but most people are just going to have a 3rd party-free, AT&T-only iPhone in their pocket when the day is through, and bricking seems to be just as common for a virgin iPhones as for jailbroken ones. As for when we'll have full use of the iPhone again is unclear, but TUAW's Erica Sadun says "don't expect a jailbreak anytime soon," which doesn't seem promising. Apparently the security is going to be a whole lot harder to crack this time around.Source: iPhone update: facts and fiction
Sad to these things come to this. but I know for sure the Dev Team will cook up something.
