The Chronic Dev Team just recently released the GreenPois0n jailbreak tool (untethered iOS 4.2.1 jailbreak) allows you to jailbreak the iOS 4.2.1 firmware on your iPhone 4, iPhone 3GS, iPod Touch 4G, iPod Touch 3G, and iPad without requiring SHSH blobs for iOS 4.2 b3. For those of you who use Ultrasn0w to unlock, remember to NOT update to stock 4.2.1 or else you will lose your unlock. Follow the guide listed below to learn how to jailbreak (untethered) your iPhone 4 / iPhone 3GS on iOS 4.2.1 using the GreenPois0n jailbreak tool.

How To Jailbreak iPhone 4 / iPhone 3GS Untethered On iOS 4.2.1 Using Greenpois0n RC5:

Step 1:

Download Greenpois0n [Download]

Step 2:

Now move the GreenPoison downloaded file on your desktop and unzip it.

Step 3:

Open the folder and double click the Greenpois0n icon to launch it.

Step 4:

Connect iPhone 4 / iPhone 3GS to the computer. Make sure the power is off and then click the large Jailbreak button.

Step 5:

Greenpois0n will display the instructions to put the device in DFU Mode. Follow the directions and you will then be prompted to press and hold the sleep button for 3 seconds.

At this point, continue holding sleep; then press and hold home for 10 seconds.

Afterwards, release the sleep button but continue holding the home button.

Step 6:

Once your iPhone 4 / iPhone 3GS is in DFU mode the jailbreak process will automatically begin.

Step 7:

Greenpois0n will now jailbreak your iPhone 4 / iPhone 3GS on iOS 4.2.1. Click the Complete! button once the software application has completed.

Step 8:

After the iPhone restarts you will notice a new Loader app on your Springboard, entitled “Greenpois0n”. Press it to launch it.

Step 9:

The next step is to press to select Cydia then press the large Install Cydia button that appears.

Step 10:

Once Cydia has installed successfully on your iPhone 4 / iPhone 3GS; you will be prompted if you want to remove Loader from your device. Press the Remove button then press the Home button. Your iPhone device will now reboot.

Note:

Poseidon: the build was put together in a rush (supposedly). Consequently, there are only a small number of people who can report back on their experience with the release. Another quick notice, Poseidon: “For anyone who gets stuck on “Initialized” you will need to hard reset your iPhone (hold home + power). Put your phone back into DFU mode but do not let go of the home button. Run GreenPois0n, release the home button when you see code running down the screen”

You have successfully jailbroken (untethered) iPhone 4 / iPhone 3GS on running the latest firmware – iOS 4.2.1.

You may also want to check out the other guides below:

For all future jailbreak and unlock software releases follow us on Twitter and/or subscribe to our RSS feed.

UPDATE:

Chronic Dev have released greenpois0n RC5_2, which fixes various bugs including the Initialized error that many users were getting with greenpois0n RC5. So if you had trouble jailbreaking your iOS device then you can try using greenpois0n RC5_2. You can download greenpois0n for Mac OSX from here.

UPDATE 2:

The Dev have released yet another update of greenpois0n RC5_b3, which fixes various bugs like the application closing on launch that many users were getting with greenpois0n RC5_b2. So if you had trouble jailbreaking your iOS device then you can try using greenpois0n RC5_b2. You can download the latest version of greenpois0n for Mac OSX from here.