First of all lets be clear that this method will only work for iPhone 3G with bootloader version 5.08 (5.8)! Otherwise, you can consider this.
You can quickly check your bootloader version by using TinyUmbrella. It should show your bootloader version right away. Alternatively, you can also use f0recast. The screenshot below shows an iPhone 3G with bootloader version 5.9.
Lets get straight to business!
- Jailbroken iPhone 3G
- Fuzzyband – install this from Cydia
- afc2add – install this from Cydia
- i-Funbox – a file explorer for iPhone, Mac users can use DiskAid
- 6.15.00 certificate (ICE2-06.15.00.cert) for Fuzzyband
- Launch Fuzzyband after installing the app via Cydia.
- Connect your iPhone to the computer.
- Launch i-FunBox and select File, then go to Applications/Fuzzyband.app, right-click and then select Copy from PC.
- Copy ICE2-06.15.00.cert you have downloaded earlier to this location
- Go back to Fuzzyband and you can now begin the downgrade process. If the downgrade is successfully, you should see “I Haz Downgrade”
- You can now unlock it with ultrasn0w and solve your GPS issue, error during restore etc.
Good luck and let us know how it goes!