rather than open new post here, have you read " newbie guide" at pinned topic..?i afraid that shifu will flame you bro, and as far as i know, there is not yet software for unlocking your iphone 3g,if the seller unlocked it for you, it means he using hardware unlocked which will make your phone sometimes no network and etc.( not stable )

try first to read pinned topic and also ask "Mr. Google" so he can tell you a lot of information rather than us..