The Dev-Team has just released the updated version of PwnageTool, which jailbreaks all 4.2.1 devices using the same untethered method that is used by greenpois0n. Also included is comex and pushfix’s patch for the iBooks anti-jailbreak code, as well as a fix for the Apple TV 2 WiFi issue. (If you are already jailbroken, these packages will be available in Cydia.)
With their permission, we’ve incorporated their 4.2.1 “feedface” untether into today’s PwnageTool 4.2. This means iPhone unlockers can safely restore to a custom 4.2.1 pre-jailbroken IPSW and retain their current baseband and unlock
The Dev-Team also notes that i0n1c has an untethered exploit ready for iOS 4.3.