Do you mean Galaxy S 3 (which is usually written III not 111)?
Is it carrier branded? Are you still on that carrier and you want to get rid of their in-house software and run a generic "stock" ROM?
Are you trying to take it to another carrier? If it is locked to a carrier, flashing a ROM will not allow it to run on another carrier... It needs to be carrier unlocked. Even that may not help. There are hardware and carrier limits as to what can be run on a network... Who is the original carrier and who is the new target carrier to move to?