Though it’s warned by the iPhone Dev Team not to upgrade your iPhone OS directly via iTunes. I’ve got quite a number of emails from iPhone jailbreakers telling that:
Oh! I accidentally upgraded my iPhone 3G to firmware 3.1 by iTunes. After upgrade, I lost the jailbreak and the unlock. Now, I can’t make call with my iPhone. Even I jailbreak it again, it still doesn’t work and with no service. Any solution?
Probably you’re facing the same problem. As you may not know, the iPhone OS 3.1 also comes with a baseband update to 05.11.07 for iPhone 3G. However, the Ultrasn0w (i.e. the iPhone unlock tool) cannot unlock this version of baseband. It can only handle the lower baseband version 04.26.08. That is the reason why we emphasize not to upgrade to iPhone 3.1 via iTunes directly, particular you need to use ultrasn0w for unlocking.
Fortunately, there is a solution for that, though not for all iPhones. Thanks for the developers of Fuzzyband Downgrader. Fuzzyband is a tool that allows you to downgrade the baseband from 05.11.07 to 04.28.06. By downgrading the baseband, you can use ultrasn0w to unlock your iPhone again.
Cool, right? There is a catch, however. Fuzzyband can only support iPhone with bootloader 05.08 (5.8) from the factory. Only a limited number of iPhones that were released in the first few weeks of the iPhone 3G production cycle were loaded with the bootloader version. For other bootloader versions, I regret that you need to wait for iPhone Dev team to release the unlock solution. Not sure your bootloader version? Fuzzyband will take care that for you and verify if your iPhone is using the valid bootloader version.
Okay, here we go. Note that this guide is for iPhone 3G ONLY.
Downgrade Baseband from 05.11.07 to 04.26.08
1. First, you need to jailbreak your iPhone. If you’re using Mac, follow the step-by-step jailbreak guide for iPhone 3.1 to jailbreak your iPhone. For Windows users, you can restore back to iPhone 3.0 OS first, followed with jailbreak using redsn0w. You can follow this downgrade guide for details.
2. Once jailbroken, launch Cydia and search for “Fuzzyband”. Then install the application.
3. After installation, go back to home screen and tap “Fuzzyband” to launch it.
4. Tap the “Downgrade” button to kick off the baseband downgrade.
Once you complete the baseband downgrade to 04.26.08 successfully, you can download ultrasn0w to unlock your iPhone. For instructions, you can follow the step by step unlock guide using ultrasn0w.
Let me know if this solution works for you. I hope Fuzzyband can help some of you to recover your iPhone, for which was accidentally upgraded to iPhone OS 3.1.