The Dev Team has just announced on the official blog the release of the ultrasn0w unlock solution compatible with basebands 05.14.02 and 05.15.04 from iOS 4.1/4.2.1 for iPhone 3G/3GS. With this unlock solution you will be able to decode any baseband from 04.26.x to 05.15.04 regardless of the iOS version you have. This unlocking solution works EXCLUSIVELY on iPhone 3G/3GS, so don't try to use it for iPhone 4 as well because it won't work. If you have an iPhone 4 then you will have to wait until an unlock solution for this terminal appears.
UPDATE: DO NOT install ultrasn0w from Cydia, it will NOT decode the baseband! You must use the new PwnageTool to update the baseband and then you will be able to decode!!!
Unfortunately the basebands 05.14.02 and 05.14.04 CANNOT BE DECODED!!!!! The only method to do decoding is by installing the baseband from the iPad in the iPhone and this is done only with a custom ipsw made with PwnageTool or using the new version of redsn0w that will be available tomorrow! If you install ultrasn0w from Cydia, IT WILL NOT HAVE ANY EFFECT on your terminals!
