I jailbroke my iphone a couple of days ago and when i plugged my at&t sim card from my other phone to the iphone i couldn't make any calls. I was then told i need to hacktivtate it. I looked it up and found ultrasn0w which this one site said worked on 3.1.2 but after trying it out it failed. Then there is blacksn0w which seemed to work in this youtube video but I don't know if it can be trusted since its not made by the iphone dev team. So how should I hacktivate my iphone 3g on 3.1.2?