While I do believe you'll receive more assistance with your iPhone over at our sister forum (www.iphoneforums.net), let me just ask - are you trying to upgrade to any other version than iOS 5.1? Because that is the newest version Apple is signing.
So, if you aren't trying to use that iOS version, try that. Anything else, again, I'd recommend you visit the iPhone forum and ask the experts over there. Here there be iPads!