A complete step-by-step guide on how to downgrade baseband version 05.11.07 to 04.26.08 for iPhone 3G in order to unlock it with ultrasn0w on iPhone firmware 3.1.

Jay Freeman (Saurik), the developer behind the infamous Cydia store for iPhone has found a way to downgrade iPhone 3GS from firmware 3.1 to firmware 3.0. This process will only work for those who have saved their SHSH to Cydia Server, for more on SHSH, read the complete detail blog post by Saurik here. Also to note here is that while this method will help you downgrade your firmware from 3.1 to 3.0, your baseband will not be downgraded which means you cant unlock it for now.