Fix iPad Baseband 6.15.00 Not Downgraded to 5.13.04 for iPhone 3GS/3G

OK, so redsn0w was released yesterday that will downgrade iPad baseband 6.15.00 to 5.13.04 but it didn’t work for some. Here’s the fix which you can try.

I tried to downgrade it while the iPhone 3GS was running on iOS 5.1.1. When the process was completed, the phone booted up but it was still showing iPad baseband 6.15.00. I found a simple solution which hopefully would work for you as well.
Firstly, use this iPad baseband downgrade guide I posted yesterday. Once done, if you still have baseband 6.15.00, try the following:
1. Build custom iOS 4.1 either with redsn0w or sn0wbreeze. You can also download custom iOS 4.1 for 3GS or you can use any custom iOS 4.x for iPhone 3G since it doesn’t require SHSH signing.
2. Put iPhone into pawn DFU either with iREB or redsn0w.
3. Launch iTunes and press Shift+Restore (Windows) or Option+Restore (Mac). Since Apple is still signing iOS 4.1 for iPhone 3GS, make sure your hosts file doesn’t point to Cydia server (though it’s OK if you have SHHS for iOS 4.1 saved there).
4. Wait until the restore is complete.
5. When your iPhone reboots, you should see your baseband is now downgraded to 5.13.04.
6. You can then build a new custom iOS 5.1.1 with sn0wbreeze or redsn0w to preserve the baseband, restore it and then unlock with ultrasn0w 1.2.7.
Pretty strange but this would work for sure.
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