The GreenPois0n untethered jailbreak for iOS 4.2.1 has been released and it allows you tojailbreak any iOS 4.2.1 device completely untethered. This will work on the iPhone, iPod touch, and iPad.

How to Jailbreak iOS 4.2.1 Untethered with GreenPois0n 1.0 RC5

Backup your iPhone or iOS device before proceeding. Do not use this jailbreak if you rely on a carrier unlock!

GreenPois0n 1.0 RC5 includes the ability to have custom animated boot logos. This version of GreenPois0n is superior to the latest Redsn0w release because it does not require developer saved SHSH blobs of 4.2b3.

Troubleshooting: If you are having problems getting Loader to download and install Cydia after using GreenPois0n RC5 jailbreak, the servers may be overloaded. In this case try again, or you can do the following: