There is a way for you to unlock your Samsung Galaxy 2 and Samsung Galaxy S3 thanks to a leaked code that has been going around but the bad news is that you will only be able to use the code if your device is still on the KitKat OS.
The code will not work on the Lollipop. The code is also believed to work on the slightly newer Samsung Galaxy s4 and Samsung Galaxy Note 3 so you might want to try it out as well although it might not work if you have upgraded to Lollipop as well.
To unlock the Samsung Galaxy Note 2 and S3, you will need to put in a new SIM card. Next, turn off the device and turn it back on. Now, open up the dial pad and key in the code *#197328640# and select  UMTS >  Debug Screen >  Phone Control >  Network Lock > Options  Perso SHA256 OFF.
You will need to wait for at least 30 seconds before pressing back to enter Main Menu. Here, you should see ” Network Lock”. Select  NW Lock NV Data INITIALLIZ.