A few hours ago Apple pushed iOS 4 final, which has the same build number as the last GM release. That means that… yep, you guessed it, you can jailbreak it with redsn0w 0.9.5b5-2. Here’s how you do it, on both Mac and Windows.
RedSn0w 0.9.5b5-2
Posted inHOWTO
iPhone DevTeam To Release RedSn0w 0.9.5b5-2
The tool will be particularly useful for iPhone 3G and iTouch 2G users who will be able to activate iOS 4 functions intentionally blocked by Apple.