My wife iphone 3G jailbroken and 3.1.2 also gets huge bills for GPRS and Edge. I checked periodically that everything is off, 3G, Edge, roaming and notification as well as set these off in Bosspref. Still last 2 months bill kena more than RM60 for those charges. Now I have to tell her not to surf if there's no wifi coz that's the culprit I think.