Chronic Dev Team has finally released the much awaited GreenPois0n RC5 which brings full untethered iOS 4.2.1 jailbreak for all iOS devices. Unlike Redsn0w 0.9.7, GreenPois0n RC5 doesn’t require you to have SHSH blobs of 4.2b3 saved on Cydia. You can jailbreak any iOS device out of the box on iOS 4.2.1 using this latest version of GreenPois0n.
Written Guide: http://tinyurl.com/4azd63z
-I recommend redsn0w tethered users to backup + restore in itunes first before trying so you don’t end up having to restore and delete everything if something goes wrong.
-3GS users with 06.15
-remember to backup anything first before trying anything
-any device with 4.2.1 will work