thats odd
Weird i've heard that the iPhone 3G is completely covered! you should check out the video by dinozambas on youtube, he shows you what to do that it is really easy to follow. If you are still having problems, try downgrading your device to an older firmware, (example, 3.1.3 3.1.2 3.0.1) and then jailbreak and unlock on those firmwares! or just keep on trying!