I had the same problem with my first s3.
Firstly,try restarting your phone or take the battery out. That may sort it out.
Secondly,update the software on the phone if you havent do so already.
If the problem presists, then take it back to the shop you got it and get a replacement. It is a software problem.
I live in the UK,i got mine from Carphone Warehouse. I rang there customer service first to see what my options was and they said take it to the store and get a replacement. They made notes on my account to say i had rung them
I took it to the store and they messed around with it trying to fix it etc. The guys were so sure it wasnt a software problem. At the time of them looking at it i hadnt told them i had talked to customer service
When they tried passing it back to me saying they couldnt do anything,i told them to look at my account and look at the notes. There faces when it said they needed too replace it was priceless.
So basically what i am saying is,ring the shop/carrier get them to make a note that the phone is faulty and take no crap from the assistant in the shops.
Then hopefully you will be able to enjoy your s3 with no problems
Hope that helps!!