Since the 2010 ruling by the U.S. Copyright Office that jailbreaking an iPhone doesn't break the law, many new users have opted to perform the operation. Many different tools exist for the job depending on the specific model and system version involved. The iPhone 3G on iOS 3.1.3 jailbreaks very simply using a program named Spirit, allowing the user to install software downloaded from places other than Apple's iTunes App Store.
Instructions
1. Connect your iPhone 3G to your computer and sync with iTunes as normal. Allow the backup process to complete fully in case anything goes wrong and you need to restore.
2. Move the downloaded Spirit program to your desktop if not already there. An error may occur if the program runs from another location.
3. Open Spirit, leaving iTunes running in the background. A window will appear displaying the model and iOS version of your device. Ensure it properly recognizes iOS 3.1.3, as Spirit will not run on newer versions.
4. Click the "Jailbreak" button and wait. Your iPhone 3G will perform the operation, which will take several minutes. Do not disconnect, turn off or otherwise disturb your iPhone during this time. When complete, it will automatically reboot.
5. Slide to unlock your iPhone after its reboot and confirm the Cydia app appears on your springboard. You may now disconnect your iPhone and use Cydia to browse and download apps and tweaks.
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