As you know Apple dropped iOS 4.0.1 for iPhone 3G, 3GS and iPhone 4 in response to wrong signal calculation. This is a minor update and no major changes in baseband update and jailbreak protection in comparison with iOS 4.0 We already posted a complete how to guide on how to Jailbreak iOS 4.0 / 4.0.1 iPhone 3GS with Jailbreakme. Following are the instructions to unlock iPhone 3GS with iOS 4.0 / 4.0.1 with Ultrasn0w.
Instructions to install ultrasn0w using cydia
Step One : Press to launch Cydia Installer from your Springboard.
Step ...