For those of you who are wishing you hadn’t upgraded to 2.2.1, iPhone hackers pH, BigBoss and EvilPenguin have creted a new tool for downgrading your baseband from 02.30.03 back to 02.28.00, restoring it’s ability to be unlocked using yellowsn0w. The hack will work on any devices manufactured prior to September 2008 with the 5.8 bootloader, though iPhones with the 5.9 bootloader cannot be downgraded.

In case you’re not sure when yours was made, you can find out by checking the serial number on the back of the device. The third, fourth and fifth digits of teh serial number show the date. If they are 8 followed by a 36 or lower (xx836xxxxxx), you should be fine. Users with the 5.9 bootloader shouldn’t have any adverse effects from running the downgrade; it should just not work for you.

The 3G BaseBand Downgrader, called 3GBBD, is available in TheBigBoss repository on Cydia.

From TheBigBoss.org:

WARNING: This tool is NOT a toy. Just use it if you can’t use Yellowsn0w on your 2.2.1 iPhone 3G. Otherwise, DO NOT INSTALL IT JUST TO TEST! YOU HAVE BEEN WARNED!

Edit: if you have bootloader 5.9, this should not cause any harm. It should simply fail. You will then have to reboot your iPhone and should be back up to where you were before running the tool.

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