Anyone who owns the Samsung Galaxy S3 or the Samsung Galaxy Note 2 will be happy to hear that unlocking the device for free is possible and you can do it right now. Once the device has been unlocked you could use it anywhere in the world and on any of the carriers, if you are not locked in to a contract.
How to unlock the Samsung Galaxy S3
If you purchased the Samsung Galaxy S3 with AT&T in the US, then right now the device will only work with the AT&T SIM card. But if you unlock it you are then able to use any SIM card. It would also be possible to send the handset to a friend or relative overseas and they could use it with the carrier of their choice.
If you want to unlock your Samsung Galaxy S3 follow the steps below.
Put a SIM card into the device that is not with your carrier. Turn off the handset and then turn it back on while the SIM card is in it. Open up the dial pad and then put in *#197328640#
Now head over to the Main Menu >  UMTS >  Debug Screen >  Phone Control >  Network Lock > Options Perso SHA256 OFF > and then wait for around 30 seconds. Hit Menu and go back and you should see Network Lock. Choose  NW Lock NV Data INITIALLIZ.
To make sure that there was no mistake the sequence you need to put in is “Asterisk Pound One Nine Seven Three Two Eight Six Four Zero Pound”. Some people call the asterisk the start key and some call the pound button the hash key.
When you have undertaken the steps above you should have unlocked your Samsung Galaxy S3 and you should be able to put in any SIM card from any carrier. Samsung have been using the code for quite some time and you may find that this will work with other devices of theirs like the Samsung Galaxy Note 2, so feel free to try it out.