Every time there is a new firmware coming out, updating puts you at risk of updating your baseband as well, making it impossible to unlock your iPhone. This time is no different than the others and many people accidentally updated their iPhone to firmware 3.1, updating their baseband to 05.11.07 at the same time.
Fortunately, there is an easy way for iPhone 3G users to downgrade their baseband from 05.11.07 to 04.26.08. Note that this is for iPhone 3G users only. If you have an iPhone 3GS, then read my article on how to downgrade the iPhone 3GS firmware from 3.1 to 3.0.
Note that this trick only works on iPhones that have the 05.08 (5.8) bootloader from the factory, which is just a very limited amounts of iPhone 3G that were released in the first few weeks of the production cycle. If you don’t know your bootloader version, you may run Fuzzyband and it will tell you what version you have and whether or not you can downgrade your baseband.
1. First, your iPhone 3G has to be jailbroken. For more information, read my iPhone 3.1 jailbreak article.
2. Launch Cydia and search for the Fuzzyband app. Install it and reboot your iPhone.
3. Launch the Fuzzyband app and tap “downgrade” to start downgrading your baseband from 05.11.07 to 04.26.08.
4. Reboot your iPhone. You should now be on baseband 04.26.08 and be able to jailbreak and unlock your iPhone using UltraSn0w.