Galaxy S3 SIM Unlock App
As of today, a new app is available in Google Play store, if you’re not willing to pay a fee and want to use your Galaxy S3 on more than one carrier.
Released by XDA Elite Recognized Developer supercurio, the new Voodoo Galaxy S III SIM Unlock app is free and will allow you to SIM unlock Galaxy S3 smartphone, though it’s in beta stage and will debut officially soon.
It’s also worth mentioning that, being in beta version, the new app will only unlock Galaxy S3 (i-9300) model.
The new app will unlock your new device’s baseband to allow access to any radio-compatible SIM cards. The app, however, back-up your important data before switching carriers but unfortunately currently it’s in beta state so you can automatically restore that data.
Head over to the Google Play store to grab this awesome SIMUnlock app. Meanwhile, make sure you have your device rooted before proceeding.
Source - Project Voodoo (direct link)