Hello All, found an article regarding an app on Google Play - Voodoo Galaxy III Sim Unlock
Free, requires root, GT-I9300 only, beta version.
First version: 1.0 beta1 of Voodoo Galaxy S III SIM Unlock tool.
This application unlocks your phone baseband so it becomes able to use SIM cards from any carrier without restriction.
Will try and give it a go soon but am busy for the next few days.