Due to battery and GPS-related problems, the baseband of the iPhone 3G may need to be downgraded. In order to downgrade the iPhone 3G baseband 6.15.00, a few tools such as Fuzzyband and iFunBox are necessary. Fuzzyband is used to determine the version of the bootloader; this has to be above 05.08 in order to proceed with the downgrade of the iPhone 3G baseband 6.15.00. A certificate for Fuzzyband will also be required. It should be noted that modifications to Apple products are not recommended and are done at the risk of the user.
After the proposed tool unlocked ultrasn0w 1.2 iPhone 3G/3GS iOS 4.1/4.2.1, the Dev Team reported that many users faced problems with low battery levels and with the position indicated by the GPS of the phone. This was due to the injection of the baseband of the iPad 15/06/2000. Moreover, it is impossible to restore your iPhone with the baseband of the iPad except with a custom firmware. A team of hackers therefore announced that it would start working on a downgrade baseband to solve the different problems. As a result, things are looking up for the iPhone 3G.
An iSpazio reader was able to find a solution to downgrade the baseband of the iPhone 3G going from 6/15/2000 (the injected redsn0w corresponds to that of the iPad) at 5.13.xx.
By following and performing this tutorial, you take full responsibility for your actions: neither ccm.net nor myself are responsible for any outcome. The method described below is here for information purposes and does not intend to encourage you to modify an Apple product.
1. Download the certificate ICE2-06.15.00.cert
2. Fuzzyband: after installing, run it and make sure it tells you that your bootloader version is 05.08. If this is not the case, you cannot perform the downgrade baseband.
3. Connect your iPhone 3G to the computer.
4. iFunBox Open, click File, navigate to the folder Applications / Fuzzyband.app. Right-click and choose Copy from PC.
5. Select the file-ICE2 06.15.00.cert previously downloaded and copy it in Applications / Fuzzyband.app.
6. Disconnect your iPhone from the computer and start Fuzzyband on your iPhone.
7. You'll see your current baseband (06/15/2000). Now you can downgrade the baseband via Fuzzyband.
It should be done. You can go check it in Settings> General> About> Prog. Modem. If you start with a 05.13 baseband, the downgrade of your baseband went well. You can now restore it if you need your iPhone with iTunes. Note that the baseband is unlocked with 05.13.xx ultrasn0w.