“An initial test version of S Voice which was found online has been blocked as Samsung Electronics does not want consumers to judge the quality of the voice feature based on a test version. When the product is launched, users of GALAXY S III will be able to fully experience S Voice.”
Users who have installed it will now get network error due to blockage. but if you want to access it and use it then you have to make some changes in the App, for this head over to here. So lets see what happens after S III launch, may be App starts working.