You don't need to reboot your device and the unlocking is almost instantly. You don't need not external tool, but root is required.
Before unlock your S 3 your important data will be backed up. Unfortunately right now there is no automatic restoration, but it seems the developer will add the feature in the next version.
Interested to unlock your Samsung Galaxy S3? Then download Voodoo Galaxy S III SIM Unlock from Google Play site below.
Download Voodoo Galaxy S III SIM Unlock.
Hope this post useful and see you again.