Here’s what you will need:
* Jailbroken iPhone 3G
* Fuzzyband installed via Cydia
* afc2add installed via Cydia
* i-FunBox (for Windows) or DiskAid (for Mac)
* Certificate to use with Fuzzyband.
And the step by step procedure is as follows:
Step 1: Download the required certificate file ICE2-06.15.00.cert from here.
Step 2: Install Fuzzyband from Cydia and start this app.
Step 3: Connect your iPhone 3G with computer via USB cable.
Step 4: Start i-FunBox and click File, then navigate to Applications/Fuzzyband.app, right-click and then select Copy from PC.
Step 5: Select the ICE2-06.15.00.cert file you downloaded earlier and then copy it to this location: Applications/Fuzzyband.app.
Step 6: Now simply disconnect your iPhone from your computer and start Fuzzyband app (which you previously installed using Cydia) on your iPhone.
Step 7: In Fuzzyband, you will now see your current version of Baseband, (which should still be 06.15.00). But now you will have the option to downgrade it to version 05.13.xx.
