I have the international version S3 and the wifi was working fine for 2 weeks then it suddenly stopped. It stays connected to the router but no internet. I tried connecting other devices to the router and they all work fine.
I tried the *#0011# trick and it didnt work for me
So i accessed the router settings and found something called DYNAMIC ROUTING which was switched off. So I turned it on et voila...wifi works again
Hope this helps you