Yesterday, the iPhone Dev Team has released a new, developers-only, version of redsn0w tethered jailbreak for iPhone 4, iPhone 3GS and iPod Touch 4G. Check the video tutorial after the break.
But first here are some very important things you should know (from iPhone Dev-Team's blog)
UNLOCKERS AND THOSE PRESERVING THEIR UNLOCKABLE BASEBANDS SHOULD STAY FAR AWAY FROM THIS! You will very likely lose your unlockable baseband if you try to install iOS 6.
THIS JAILBREAK IS INTENDED ONLY FOR DEVELOPERS OF JAILBROKEN APPS! There are just too many broken components (Apples official apps, 3rd-party App Store apps, Cydia apps, etc) for this to be useful to anyone but those truly looking to fix bugs in their iOS 6 jailbroken apps.
CYDIA WILL NOT BE INSTALLED because it just hasnt had time to be updated to the new SDK. The only access you'll get to the device is through SSH or afc2. If you don't know what either of those are, you shouldnt be using this developer version of redsn0w!
THIS REDSN0W WILL NOT HACTIVATE! You need to be an iOS developer with a registered UDID to get past the activation screens. PLEASE DONT PIRATE APPLE SOFTWARE! Only registered devs with Macs can develop iOS applications,and only those people will have legitimate access to the beta IPSWs.
THIS IS A TETHERED JAILBREAK ONLY! No new exploits are being exposed with this jailbreak (it uses geohots limera1n bootrom exploit), but that comes at a cost. You will need to use redsn0w's "Just boot" button to be able to use many things, including Safari. If you see Safari or iBooks crash when you open them, its because you didnt boot tethered.
You must point redsn0w at your IPSW the first time you "Jailbreak" and "Just boot" tethered because that IPSW is only available to developers, and redsn0w cant automatically fetch the pieces it needs from it. By the time youve done a 'Just boot' tethered JB though, redsn0w has cached all the files it needs from the IPSW so you wont need to point redsn0w at it any longer.
If you still think that is worth to jailbreak your device check this tutorial
[Read the original blog post]