The Dev Team just updated RedSn0w to version 0.9.6b4, which will jailbreak iOS 4.2.1. As we explained yesterday, thanks to a combination of pwnage2 exploit, the arm7_go exploit, 24kpwn, and LimeRa1n, you will get an untethered jailbreak for iPhone 3G, older iPhone 3GS, and non-MC iPod touch 2G.

Unfortunately, other devices will get a tethered jailbreak, which means you will have to plug your iPhone in and launch RedSn0w every time you reboot…

It is very important to note that if you want to unlock, you should not use RedSn0w as it will update your baseband. Wait for PwnageTool to update safely without updating your baseband.

You can download RedSn0w 0.9.6b4 for Mac or Windows from our iPhone downloads section. We now have a RedSn0w tutorial up on the blog.