Galaxy S2 SIM Unlock code finder will find the SIM unlock code for your device, or the unfreeze code. It'll take a few minutes to run, but you should end up with the code to SIM unlock your device.
If the code doesn't work, don't keep trying it !. You may end up with a freeze. In that case, the program can also find the unfreeze code, but if the SIM unlock code is wrong in the first place, maybe so is the unfreeze code.
The app need root so be sure your SGS2 is rooted.
On some newer SGS2 devices, it does not work at all. You can try "Galaxy_S Unlock" app, but beware this unlock method is much more dangerous !!!
Download Samsung Galaxy S 2 SIM unlock code finder from here