Requirements:

• iOS 4.2.1 original firmware of your device saved on your computer (Download Here)
• iTunes 10.1.2 installed on your Mac (Download link)
• Download PwnageTool 4.1.3 for Mac

Modifying PwnageTool

Step 1: Download PwnageTool bundle (via) for your iPhone 4 device. Extract the .zip folder, and copyiPhone3,1_4.2.1_8C148.bundle to your desktop.
Step 2: Download PwnageTool 4.1.2 and copy it to your desktop. Right click, and then click on "Show Package Contents”
Step 3: Copy the .bundle files to PwnageTool.app/Cont ... Read more »