We just told you about the announcement by the iPhone Dev Team about the release of latest Redsn0w update. Here’s the complete Guide to Jailbreak iOS 4.2.1 on any iOS device be it iPhone, iPod Touch or iPad.

Important Note: Unlockers relying on Ultrasn0w should not proceed as there is no unlock for iOS 4.1 or 4.2.1 available yet. It should be here in a week’s time though.

Firstly, you will need to update your iOS Device to the latest iOS 4.2 firmware in case you haven’t done that. In order to do so, update in iTunes or head over to the link below(for direct download links) and download the .IPSW firmware file. It’s better you download the .IPSW file using direct links as you will require it during jailbreak.

Direct Download Link Apple iOS 4.2

You should then update your device in iTunes by pressing Alt + Update(Shift+Update in Windows).

Tip: Please save your SHSH while you are still on 4.1 or lower firmware. Instructions here.

Steps to Jailbreak iOS 4.2.1:

Now continuing with the iOS 4.2.1 Jailbreak, download the latest version of Redsn0w for your Operating system here.

﻿Mac OS X

Windows

Extract the Redsn0w archive and run the Redsn0w app.

Now click on Browse and point it to the iOS 4.2 firmware file you download in the previous steps.

Once the IPSW is identified hit next and let Redsn0w prepare Jailbreak data.

Once the next page appears tick the checkbox beside install Cydia and hit next.

The rest of the steps are displayed on screen. Connect your iPhone to the computer and then turn it off and hit Next.

Hold the Home and Power button together for 10 seconds. Release the Power button while still holding the Home button for a few seconds. Click Finish when the app is done jailbreaking. You should see some lines of code on your iPhone screen during this time.

Important Note:

The Dev Team has not been able to make an untethered jailbreak for the latest generation devices yet. So type of jailbreak depends on device you own.

iPhone3G, older iPhone3GS, and non-MC iPod touch 2G: untethered jailbreak

More recent devices (iPhone 4, iPad, iPod touch 4G): tethered jailbreak (meaning if your device reboots, you’ll have to re-jailbreak)

If you have a device listed in second point, it is very likely that cydia won’t start after jailbreak. So repeat the above steps and Select “Just boot tethered right now” and all should be fine until you restart your device. You will just have to repeat this step again.

If your device falls in the first category no need to worry.

Feel free to ask via comments in case you have a question.