so I bought an iphone 3g from ebay. it is jailbroken because it has cydia. it is also running 2.2 fw. It is NOT unlocked as far as I can tell and when I put the sim in from my other iphone I don't get any signal? It doesnt say invalid sim or anything... could the iPhone be trash or do I just need to rectivate the sim with at&t on this iphone to get it to work? I havent synced or anything with the phone yet if that helps. thanks for any and all suggestions!!!