The iPhone Dev Team have released the PwnageTool 4.2 version to do untethered jailbreak on the iPhone 3G, 3GS and 4, iPod Touch 3G and 4G, iPad and Apple TV 2G on iOS 4.2.1 firmware. PwnageTool 4.2 uses the same exploit used by the Chronic Dev Team in the GreenPois0n tool.

Download PwnageTool 4.2

PwnageTool 4.2 helps to jailbreak iOS 4.2.1 untethered along with preserving the baseband so that you could unlock your iPhone using Ultrasn0w 1.2.

Download PwnageTool 4.2 from here