Untethered Jailbreak is Working on iOS 4.2.1
Comex has a untethered jailbreak working for iOS 4.2.1. We still don’t know when it will be released to the public, but progress is being made.
The video shows a jailbroken iPhone 4G with iOS 4.2.1 booting without the use of a computer, meaning it’s untethered.
In the meantime, redsn0w already gives tethered jailbreak for 4.2.1