This guide is for those who have iPhone 3G and 3GS with firmware 3.1.3 who have jailbroken their iphones with Redsn0w or blackra1n as both of these tools upgrade the baseband so the baseband should be 05.11.07 and make sure you check the baseband version before you proceed with the tutorial below.
Unlock iPhone 3G, 3GS With 3.1.3 at 05.11.07 Baseband
1. Firstly Download Redsn0w or blackra1n to jailbreak your iPhone 3G & 3GS 3.1.3 Firmware
In order to install this latest stable version of blacksn0w and unlock your iphone 3g and 3gs, follow the step by step procedure given below.
2. Start cydia on your iphone
3. Tap manage tab at the bottom
4. Now tap Sources and then tab edit and then add button to add the following repository
5. Now it will add the repo and update the repository, then tap the button return to cydia
6. Now search for blacksn0w RC2
7. Install it and restart your phone, and insert any SIM card you will see the signal, your iPhone is now unlocked.
[ Source GetMeApp.com ]