Apple released new iOS 4.2.1 firmware for iPhone 3G, 3G S and iPhone 4. The iOS 4.2.1 firmware includes multi-tasking, folders, Game Center, AirPlay, AirPrint and several other additions. All those who are using an iPhone 3G or 3G S unlocked versions can now upgrade to iOS 4.2.1 firmware as iPhone-Dev has released new jailbreak and unlock tools. The new Redsn0w 0.9.6 b6 is a tethered jailbreak for iPhone 4, iPhone 3G S new model and un-tethered jailbreak for iPhone 3G and iPhone 3G S old models. That means, all iPhone 3G and 3G S (old bootrom) users can use the latest Redsn0w jailbreak and proceed to Ultrasn0w unlock from Cydia.
Unlock iPhone 3G and 3G S firmware:
Windows users can download Redsn0w 0.9.6b6 to jailbreak iPhone 3G and 3G S on iOS 4.2.1 firmware and activate it using the SAM repository from the Cydia. This method is the best method to unlock iPhone 3G or 3G S in iOS 4.2.1 firmware.This is because here the activation is done using the method that is very similar to the official activation. We will get our Push notifications working and improved battery life also.
Another method is hactivation though Ultrasn0w 1.2 after a jailbreak using Redsn0w 0.9.6b5 and PwnageTool 4.1.3 for (Mac). Here we upgrade the baseband of the iPhone 3G or iPhone 3G S using the iPad baseband and use a vulnerability in that baseband to unlock the device using Ultrasn0w 1.2 in Cydia.
A proper iPhone 4 iOS 4.2.1 firmware jailbreak or unlock is not available at the moment.