The iPhone Dev Team has just released Redsn0w 0.9.6b3 which brings support for iOS 4.2.1 GM firmware file. The highlight feature of this release is SSH and SSL support which will now allow you to install bundles and packages independent of Cydia, which is currently broken on 4.2.1.
This release is mainly geared towards developers who wants to get their jailbreak-apps ready just in time for iOS 4.2.1 release.
The instructions to jailbreak iOS 4.2.1 GM with Redsn0w 0.9.6b3 are exactly similar to the last release.
Follow our complete step by step guide posted here to jailbreak your iOS device on iOS 4.2.1 firmware.
NOTE: All iPhone unlockers must STAY AWAY from Redsn0w. Redsn0w 0.9.6b3 supports tethered jailbreak only.