So, here is a guide on How to unlock iPhone 3G,3GS 3.1.2 Firmware using Ultrasn0w.

Before attempting to unlock your iPhone 3G/3GS make sure you have update and jailbroken your iPhone with 3.1.2 Firmware and make sure you have install Cydia at the time of jailbreaking.

1. Once you have jaikbroken your iPhone 3G/3GS open Cydia on your iPhone.
2. Now select on Manage tab at bottom and choose Sources.
3. Now you will have to add repository, to do this tap on edit and then Add button now type following repository URL

   http://repo666.ultrasn0w.com/

4. After the source has been added tap on “Return to Cydia”.
5. Now go to Search menu from bottom menu, type “ultrasn0w” and press search.
6. Now tap on the ultrasn0w and choose Install from the top right menu.
7. After installation complete restart your iPhone and insert your SIM.
8. Here you go, now your iPhone 3G/3GS is completely unlocked and ready to use with any carrier.

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However, I would like to share a
guide on how to jailbreak iphone 3Gs 3.1 firmware on Windows using Custom Firmware (iPhone2,1_3.1_7C144_Custom_Restore).

How to Jailbreak iPhone 3G Firmware 3.1

1. First Download the following links of custom iPhone 3.1 Firmware
2. Now join all the downloaded parts using HJSplit and you will get one archive, uncompress that archive and it contains IPSW file of firmware 3.1
   Custom iPhone 3GS 3.1 Firmware Part 1
   Custom iPhone 3GS 3.1 Firmware Part 2
   Custom iPhone 3GS 3.1 Firmware Part 3
   Custom iPhone 3GS 3.1 Firmware Part 4
3. Now Install (if you haven’t already) and open iTunes 9
4. Connect you iPhone to the PC using data cable.
5. Choose your iPhone from devices menu on left.
6. Now click “Resotre” while holding Shift key and select the custom IPSW file which you downloaded in step 1
7. Now Sit back and relax until the installation process complete.
8. After Jailbreaking your
   iPhone 3GS to 3.1 Firmware you can follow this guide to unlock you iPhone and use with any SIM/Carrier.

iPhone 3GS on firmware 3.1 using this latest release. However Pwnage Tool 3.1.3 will only be able to jailbreak those

iPhone 3GS and iPod 2G who have already been jailbroken previously and will not work for those one with a 3.1 firmware just unboxed.

They have also provided a list of important points which you should consider to read before using Pwnage

1. If you are using a 3G iPhone with ultrasn0w and rely on ultrasn0w to obtain cellular service, then you should only upgrade to 3.1 with a PwnageTool created .ipsw.
2. PwnageTool will work for the
   iPhone 3GS assuming you have already Pwned it at 3.0 or 3.0.1
3. PwnageTool will work for the iPod touch 2G assuming you have already Pwned it at 3.0 or 3.0.1

Step by Step guide on how to Jailbreak

Download Pwnage Tool 3.1.3

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