Before you start with it here is what you’ll need in this guide.

1. iTunes 9
2. Pwnage Tool 3.1.4
3. Download Original iPhone OS 3.1.2 Firmware

How to Jailbreak iPhone 3G 3.1 Firmware:

1. Download and Install iTunes 9 from Apple site.
2. Make complete backup of your iPhone.
3. Download Original iPhone 3.1.2 Firmware using the links provided in this post.
4. Download Pwnage Tool 3.1.4 and select your device from devices list.
5. Now Pwnage tool will automatically detect original
   firmware file which you downloaded in Step 3, if it can’t then browse it manually.
6. Click Next and then Choose Yes and then on another dialogue box Choose no, if you aren’t using Contract iPhone. Choosing No will let you unlock your iPhone and use it with any SIM
7. Now Pwnage Tool 3.1.4 will start building custom IPSW file.
8. Once done, click Yes and then click Next.
9. Now Open iTunes 9 and choose your iPhone from the devices list on left side now press Alt/Option key and then click on Restore and browse the Custom made iPhone 3.1.2 firmware now choose Open.
10. Now relax back until iTunes updates your iPhone to 3.1.2 Firmware.

After completing the entire above steps your iPhone 3G 3.1.2

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