3G FuzzyBand Downgrader is a safer iPhone 3G Baseband Downgrader as this one detects your baseband and bootloader version and does the right thing first. Fuzzyband Downgrader has been updated to include downgrading support from the iPhone OS 4.0b1 baseband 05.13.01 for iPhone 3G with bootloader 5.8 Fuzzyband Downgrader detects your bootloader and baseband and downgrade it with a simple click. Note that 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. 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.
Once you downgrade your baseband you can unlock again with good old Blacksn0w.