Download GreenPois0n RC5 Beta4 to Untethered jailbreak iOS 4.2.6 Version iPhone 4. If you need to jailbreak your iOS 4.2.6 version iPhone 4, but need no unlock, this tutorial is for you. If you rely on unlock, refer to
[Guide] Download PwnageTool 4.2 to Untethered Jailbreak iOS 4.2.1 iPhone 4/3G/3GS, Version iPhone 4.
iOS 4.2.6 Version iPhone 4 untethered jailbreak with GreenPois0n RC5 Beta4 is easy thanks to Chronic Dev Team. Follow the steps below both on mac and windows.

Step 1: Download iTunes 10.1 or later to backup all your contacts and messages, apps, music,etc.
Step 2: Download official iOS 4.2.6 from apple.
Step 3: Download GreenPois0n RC5 Beta from www.GreenPois0n.com.
Step 4: Launch GreenPois0n. And connect iPhone with computer.
Step 5: Click "Prepare to Jailbreak (DFU)" and follow the steps on the screen to enter the DFU mode.
Step 6: After enter the DFU mode, Click "Jailbreak" icon to start jailbreaking. When the jailbreak process finished, just close the GreenPois0n.
Step 7: After the reboot, run the app Loader to install cydia.
This steps is almost the same on both windows and mac. But you have to download the GreenPois0n RC5.4 for windows/mac.
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