If you upgraded iPhone firmware 3.0 beta accidentally, you may want the Fuzzyband Downgrader which can be found in Cydia. After users upgraded to iPhone firmware 3.0 beta, the baseband will be upgraded to 04.26.08. It cannot be software unlocked by the yellowsn0w solution. The Fuzzyband Downgrader will help to do it easily. But, note it only works with the iPhone 3G that have the old bootloader 05.08. Well, just download it first, and see if you are lucky or not.
