How to jailbreak and unlock iPhone 3G with firmware iOS 4.0.1

There is no official jailbreak utility for iOS 4.0.1. However you can still jailbreak and unlock iPhone 3G. Just do the following:

• Download the latest RedSn0w 0.9.5-b5 in our utilities page here.
• Download firmware images for iOS 4.0 here.
• Run RedSn0w and point it at the 4.0 IPSW. (Yes – point it at the 4.0 IPSW even though you're at 4.0.1). This will also hacktivate your iPhone3G at 4.0.1 if you haven't already been activated by iTunes.
• Install ultrasn0w in Cydia (add repository http://repo666.ultrasn0w.com) if you need a carrier unlock (and in the USA, remember to turn off 3G mode in Settings→General→Network).