Unlocking Samsung Galaxy S II is never been so easy with application developed by XDA-developers. This application will allow you to unlock the the SIM, that will allow you to use any SIM card with your Galaxy S II. Specially if you want to use the phone with with a different carrier. Galaxy S2 SIM unlock will look for the SIM unlock code for you. You can enter the code when the phone request unlock code, when you use the phone with a different SIM card.
You can easily find the app in the Google Android market for free under the name [ROOT] Galaxy S2 SIM Unlock. If you want to unlock your Galaxy S2 then this would be the solution.