This Tutorial will show you how to Carrier Unlock Iphone to use it with any GSM SIM.
Once you Iphone is Jailbroken you will have an Cydia Icon on your iphone desktop
Open Cydia and click the manage icon at the bottom.
Click the Sources button
An UltraSn0w Repo will be present, and if it is there the jump to the next step otherwise continue.
If Untrasn0w is not there you will need to add it by clicking the edit button on the right top. Now press ADD button on top left. Enter http://repo666.ultrasn0w.com/and press the Add Source button. After adding click Return to Cydia. Click Done tab at the top right.
Now go inside the repo666.ultrasn0w.com from the list and select the UltraSn0w Package. Click the INSTALL tab on top right of the screen. Once its done you need to restart the springboard and
Now your phone is Carrier unlocked.