Now using Sn0wbreeze 3.1.3 you can unlock your iPhone 3G/3GS 3.1.3 with Ultrasn0w 0.92. This will only work if you haven’t updated to stock firmware 3.1.3. The procedure to unlock
1. Download Sn0wbreeze 3.1.3 and jailbreak your iPhone 3G & 3GS 3.1.3 OS for iPhone 2G 3.1.3 you can use Redsn0w 0.9.3
2. Once you have jailbreaked your iPhone 3.1.3 you can go to Cydia under manage tab then access sources. (T-Mobile users should disable 3G before installing Ultrasn0w)
3. Now edit and add http://repo666.ultrasn0w.com source url and click on Add sources.
4. Now search for ultrasn0w 0.92 and install it. It will automatically unlock your iphone.
5. Now restart your iPhone and enjoy unlocked iPhone 3G/3GS 3.1.3