Server-Side

Download these files:
iPhone 3G (Legit AT&T) – http://www.demonoid.com/files/details/1965353/2325666/
iPhone 2G (Legit AT&T) – http://www.mininova.org/tor/2700484

Put your iPhone in DFU mode:

1.) Sync your phone/back it up with iTunes one last time.
2.) Turn off the phone.
3.) Turn the phone on holding both the Power and Home button. Once it powers on, continue holding the Home button until you see the graphic that says you need to plug the phone into iTunes.
4.) Shift-Click Restore in iTunes for the iPhone, select the custom firmware that you downloaded.
5.) iTunes will guide you from there. Good Luck!