GreenPois0n RC5 RC6 Final is finally released and provides untethered iOS4.2.1 jailbreak for iPhone, iPad, iPod Touch G3/G4 and Apple TV. It does not require the iOS 4.2b3 SHSH blobs, and right now ONLY works with Mac OSX operating system (Windows version to come very soon can be downloaded here). GreenPois0n RC5 RC6 Final will also support animated custom boot logo on iPhone, iPad and iPod touch.
Download here for the Mac OSX version. The steps are straight forward. Simply follow the on-screen instructions. Once installed, you will see Loader app on the home screen. Launch it to begin installing Cydia (WiFi required).
Note: For those who are new to jailbreaking and unlocking, this will only jailbreak your device, not unlock it. We’re still waiting for the unlock for iPhone 4 with baseband 2.10.04, 3.10.01 and 4.08.00.