These are instructions on how to jailbreak any iPhone (including the iPhone 4) on iOS 4 using JailbreakMe by Comex. Before beginning make sure your device is activation on iOS 4.0.0 or 4.0.1.
Press to launch Safari from your Springboard.
Press to select the address bar and input http://jailbreakme.com then press the Done button.
To begin the jailbreak simply move the slider to right.
You will be displayed a status bar as the download progresses.
Once the download is complete the jailbreak process will begin
Once you are notified that the jailbreak process is complete press the OK button.
Press the Home button to reveal Cydia on your desktop!
Congratulations you are done! You may now continue by installing UltraSn0w to unlock you device. iPhone 4 users still need to wait a bit for an UltraSn0w update which will arrive shortly.
A big thanks goes to Comex and the iPhone Dev-Team for their efforts and successes.