IOS 4.2.1 on iPhone 4 is finally be untethered jailbroken. With this method (untethered jailbreak), you don’t have to boot up your iPhone with redsn0w every time it has been restarted or the battery is drained. The latest release of greenpois0n allows you to untethered jailbreak your iPhone 4, if you have not update your iPhone 4 to IOS 4.2.1, you can take this opportunity to do so and still enjoy the advantages of using jailbroken iPhone. Before you proceed to the step-by-step guide, it is recommended that you backup or sync your iPhone 4 with iTunes. Then, download greenpois0n and IOS 4.2.1 at the downloads page. Once you’re done, let’s get started.
1. Make sure your iPhone 4 has IOS 4.2.1 installed, you can check the version at Settings, General and About. If your iPhone 4 has lower version, simply update your iPhone 4 through iTunes to IOS 4.2.1.
2. Connect your iPhone 4 to computer using USB cable and switch it off. Now, launch the greenpois0n.
3. Click the “Prepare to Jailbreak (DFU)” button, follow the on-screen instruction to put your iPhone 4 into DFU mode.
4. Once the iPhone 4 is in DFU mode, greenpois0n will proceed to jailbreak process and you’ll see the codes scrolling on your iPhone. It will reboot after the jailbreak process is completed.
5. Start the Loader application (green icon on the SpringBoard), and follow instructions to install Cydia. The iPhone should reboot after Cydia is successfully installed.
6. To remove the icon, start the loader again and tap Remove Loader.app from the Option button. The iPhone will respring.
Well, I hope you will find this guide useful and enjoy the jailbreaking processes. As always, you can post any question about the jailbreak on the comment section.