This is the Gold Master of OS 3.0 for iPhone, it doesn't require you to be a developer to install and use it. I'm not a dev and it works for me.
Make sure you have iTunes 8.2 installed.
More info on OS 3.0:
http://www.apple.com/iphone/softwareupdate/INSTALLATION INSTRUCTIONS:
1. Download and extract the files below
2. Open iTunes and connect your phone
3. Option click on Restore and Select the ipsw file you just extracted
4. Let iTunes do it's thing.
DOWNLOAD:
http://rapidshare.com/files/242992085/iP3GOS3.part1.rarhttp://rapidshare.com/files/242997529/iP3GOS3.part2.rarhttp://rapidshare.com/files/243002036/iP3GOS3.part3.rar