Dev-Team has release RedSn0w 0.9.6b4 to jailbreak iOS 4.2.1 on iPhone 4, 3GS, 3G, iPod touch 4G, 3G, 2G and iPad.One day after the release of iOS 4.2.1 for Apple’s iPod Touch, iPhone, and iPad, the mobile software has already been jailbroken using the newly-released Redsn0w 0.9.6b4 update.
Download links (new links added):
Windows (Alternate Link)
Macintosh (Alternate Link)
The jailbreak is tethered. What that means is that if your device somehow loses power or is rebooted, you’ll need to get it in a jailbroken state once again by plugging it into your computer. It’s, for sure, not the most convenient of jailbreaks, but it’ll certainly do why we wait for an untethered jailbreak. Word is that one is in the works right now, and should be released in the coming weeks.
RedSn0w 0.9.6b4 jailbreaks iOS 4.2.1 with working Cydia and MobileSubstrate. Step-by-step instructions on how to jailbreak iOS 4.2 with RedSn0w 0.9.6b4