How to: Jailbreak iPhone 4 on iOS 4 / 4.0.1 using JailbreakME 2.0
Now you can jailbreak any iPhone (including iPhone 4), iPod Touch or iPad on all Firmwares.
Steps:
Step 1: You just need Wi-Fi network, Navigate your Mobile Browser Safari to http://jailbreakme.com and then touch and slide to jailbreak.
Step 2: Now Have fun, You got a jailbroken iPhone 4 as mine: