STEP 1: Download & install the latest version of iTunes & make sure your device is not on iOS 4.1 (links at the bottom).
STEP 2: Start iTunes, connect your device to your computer via USB and sync your iPhone then back your data.
STEP 3: Start PwnageTool and select your devices (iPhone 4 used in this guide).
STEP 4: PwnageTool should automatically detect the correct iOS firmware for your device.
STEP 5: On seeing this message, hit "No" to preserve your baseband to be able to unlock.
STEP 6: PwnageTool will start creating the custom pre-jailbroken firmware for your device.
STEP 7: Follow the instructions seen on the screen to enter DFU mode as shown in the screenshot below:
STEP 8: Now, You will have to restore your iPhone to the jailbroken custom firmware by Clicking on the iPhone icon on the left sidebar of iTunes then hold left “alt” button (“Shift” button on Windows) on the keyboard and then click on “Restore” then release the alt button, Now Select the custom firmware created by Sn0wbreeze and Let iTunes go in a bunch of steps.
STEP 9: Now, i't unlock time! In case you preserved your device's baseband, you can use our steps to unlock iPhone 4, 3GS, 3G using Ultrasn0w 1.0-1 :
Step 1:You have to jailbreak your iPhone 3G and iPod Touch 2G on iOS 4.0.2 with Redsn0w.
Step 2:You have to activate iPhone 3G.
Step 3:Now you are able to unlock your iPhone 3G using ultrasn0w from Cydia.
