Well wouldn’t you know it, iPhone OS 4.0 isn’t available just yet but apparently according to an article over on gizmodo the iPhone 4.0 jailbreak tool is already available for the iPhone 3GS.

Word has come down from the guys at iphwn that The Dev Team has now made the redsn0w 0.9.5 BETA download available, however it does come with a warning that redsn0w 0.9.5 Beta is not intended for the end user.

Redsn0w 0.9.5 is meant for developers and allows the devs behind jailbroken applications to fix their software before the iPhoning public get hold of iPhone OS 4.0, and as redsn0w 0.9.5 is meant for jailbroken application developers the beta doesn’t perform hactivation.

Basically you’ll need a registered developer UDID with Apple if you want to get past the activation screen, and they say for similar reasons there is no Windows version.