Now that you already have jailbroken your iPhone here you will learn how to unlock your iPhone 3G and 3GS if you haven't jailbroken yet, click here to learn how to jailbreak your iphone.

Follow these steps to unlock your iPhone.

1- Launch Blackra1n app.

2- Touch Cydia and then tap Install

3- Launch Cydia. (At first launch you might get a message Reorganizing and will close after that, you will have to relaunch cydia)

4- Tap on Manage.

5- Tap on Sources

6- Then tap on Edit

7- Then tap on Add.

8- Enter http://blackra1n.com now tap Add Source.

9- Cydia will update the sources

10- After that tap on Return to Cydia

11- Now tap Done

12- Tap Blackra1n.com

13- Tap blacksn0w

14- Now tap Install

Now Cydia will install it and your iPhone is unlocked. Congratulations.

15- Restart iPhone and you are done.