Most of iPhone 3GS and iPhone 3G users upgraded their baseband to iPad’s one which is 06.15.00 (that is how to unlock iPhone 3GS and 3G). The following method will help you to downgrade the baseband of iPhone 3G from 06.15.00 to 5.13.xx, which is unlockable using Ultrasn0w. This method will allow you to restore your iPhone 3G back to the official stock firmware through iTunes which is not possible on iPad’s 06.15.00 baseband.
This is not an official method from the Dev Team (they are working around the clock to realize a much easier solution for downgrading 06.15.00 baseband to lower basebands on both iPhone 3G and iPhone 3GS). Please note, this solution only works on iPhone 3G bootloader 5.8. Here is the detail step-by-step guide by RedmondPie:
What you need in order to downgrade 06.15.00 baseband to 05.13xx on iPhone 3G?
- Jailbroken iPhone 3G
- i-FunBox (for Windows) or DiskAid (for Mac)
- Fuzzyband installed via Cydia
- Certificate to use with Fuzzyband
1. Download the required certificate file ICE2-06.15.00.cert from here.
2. Install Fuzzyband from Cydia and start this app.
3. Connect iPhone 3G to you computer through USB cable.
4. Initiate i-FunBox. Click on File, then browse to Applications/Fuzzyband.app. right-click and then select Copy from PC.
5. Select the ICE2-06.15.00.cert file you downloaded in step 1. Copy it to the following location:Applications/Fuzzyband.app.
6. Disconnect your iPhone from your computer and start Fuzzyband app (refer step 2) on your iPhone 3G.
7. In Fuzzyband application, you should see your current version of Baseband, (should be 06.15.00 still) and you have the option to downgrade it to version 05.13.xx.
Once the downgrade process is completed, Go to Settings –> About and check whether your 05.13.xx baseband is already there. You are done – so no more error when you want to update or restore any firmware.
