I tried SIM unlock with ultrasn0w, but it seemed not working. Even more it made my iPhone just a block. :-( Maybe, it could be working with other SIM cards. But, I couldn't try, since I don't have any other SIM.
After this disaster, I restored my iPhone with iTune restore.
For more information: http://www.ihackintosh.com/2009/10/how-to-unlock-iphone-3gs-os-3-1-with-ultrasn0w/