Geohot released the all-in-one iPhone jailbreak tool blackra1n late last year. Apple previewed iPhone OS 4.0 last Tuesday. Many people afterwards asked, “when will 4.0 be jailbroken?” Well, it already has been!
Clicking on the image link showed an iPhone running OS 4.0 with both blackra1n and Cydia icons:
The cat and mouse game continues between Apple and these iPhone ‘freedom fighters’. Expect updated releases to come soon, probably after 4.0 is released to prevent patches from Apple.