After the launch of their ultrasn0w iOS 4 unlock, the iPhone Dev Team has now released PwnageTool 4.0 for jailbreaking aficionados out there looking for a way to hack open the latest iPhone firmware from Apple. Just like the iOS 4 update, this new jailbreak tool only works with the iPhone 3G and iPhone 3G S. However, apart from that restriction, there are additional limitations to this iOS 4 jailbreak. For the iPhone 3G S, only units that have been previously jailbroken and with an old bootrom are compatible with this new PwnageTool. iPhone 3G units that have been jailbroken with the use of the Spirit jailbreak aren't supported here.
For the full set of reminders and precautions as well as a list of links where you can download PwnageTool 4.0 from, simply head on over here to the iPhone Dev Team’s blog for more info.
UPDATE: The iPhone Dev Team has updated this iOS 4 jailbreak to PwnageTool 4.0.1 to address a known issue concerning the iBooks app.