Fuzzyband, the utility with which you can downgrade anyone's baseband iPhone 3G cu boot loader 05.08 is also compatible with iPhone OS 4.0 beta 1, if you have one iPhone 3G with the respective baseband you can downgrade from baseband 05.13.01 la 04.26.08 and you can use ultrasn0w to decode the phone.
If you don't know which bootloader your phone has, you can download it fuzzy band from Cydia and the application will tell you if your phone has that or not bootloader but I'll spare you an extra job and tell you that if your phone was bought after September 2008, then it definitely does NOT have boot loader 05.08 but a higher one, so it is incompatible with fuzzy band.
I remind you that Fuzzyband works DONATE cu iPhone 3G cu boot loader 05.08, NU works with iPhone 3GS in no way and there is NO other way to downgrade baseband.
