Downgrade iPhone 06.15.00 Baseband to 05.13.xx (iPhone 3G with Bootloader 5.8 Only)

An iSpazio reader found a method to perform the baseband 06.15.00 downgrade on iPhone 3G with Bootloader 5.8 In case you updated your iPhone 3G with Baseband 06.15.00 With Redsn0w trick and now wants to go back to stock baseband, following is the guide for you.
Fuzzyband Downgrader detects your bootloader and baseband and downgrade it with a simple click if your bootloader is vulnerable to Fuzzyband . Fuzzyband Downgrader available in Cydia, just refresh your sources and search for Fuzzyband and install the application. But you need to do little more effort with fuzzyband and following are the step by step instructions.

Please Note :

• Downgrading works from any version greater than 05.13.xx It will put your baseband back at version 05.13.xx which is hackable by ultrasn0w.
• Downgrading only works on iPhone 3G with 05.08 (5.8) Bootloader from the factory. This is a very limited number of phones that were released in the first few weeks of the 3G production cycle.
• If you do not know your bootloader then you can run Fuzzyband and it will report the version number for you.
• iPhone 3GS and large numbers of iPhone 3G aren’t supported by the Fuzzyband, so in case your baseband is updated then wait for Dev team/GeoHot to release any workaround. This may take weeks or months.

This is what you need to have:

• iPhone 3G Jailbroken
• Fuzzyband installed via Cydia;
• afc2add installed via Cydia;
• iFunBox (for Windows) or DiskAid (for Mac);
• certificate for use with Fuzzyband Download it HERE

This is what you need to do:

1. download the certificate from 06.15.00.cert ICE2- HERE;
2. Install fuzzyband through cydia,
3. connect the computer to the iPhone 3G,
4. Start iFunBox and click File, then go to Applications / Fuzzyband.app, drap and drop the file you downloaded (ICE2-06.15.00.cert);
5. At this point you must disconnect the iPhone from your computer and start Fuzzyband (which you previously installed from Cydia);
6. in Fuzzyband you will see your current version of the baseband (which should be 6.15) and have the opportunity to downgrade to version 5.13.
7. Now just click on downgrade baseband, thats it!

Once you have downgraded, Go to Settings –> About, and scroll down to check your Baseband which should now read 05.13.xx. Now just go to cydia and install ultrasn0w, thats it!
But, remember to repeat the same  process if you update your iphone 3g.