The PwnageTool 3.1.3 allows you to jailbreak iPhone 3G 3.1 firmware. But still if you want to use any other SIM than AT&T, you have to unlock it. But you don’t have to become disappointed or sad because here’s a tutorial or guide to unlock your iPhone 3G 3.1 firmware with the help of a software called Ultrasnow.
1. Make sure that you have updated your iPhone 3G to 3.1 firmware, installed Cydia and jailbroken it. If you have done this, proceed.
2. In your iPhone, open Cydia.
3. Choose Manage tab at the bottom.
4. Select Sources.
5. Tap on Edit and then add button to add repository.
6. Type the URL ‘ http://repo666.ultrasn0w.com/ ‘ and add it.
7. Choose ‘ Return to Cydia ‘ option.
8. Choose select option from the menu at the bottom.
9. Search for ‘ utrasnow ‘.
10. Open ultrasnow and install it.
11. Restart your iPhone and put the SIM card in.
That’s all! Your iPhone 3G is ready to go.