S Voice doesn't work that well for me. It has a habit of cutting me off mid sentence and when it does work it is often very slow.
Here is a way to to access google voice search directly by double clicking the home button. (I didn't see that this had already been posted).
http://sgs3mod.blogspot.com/2012/07/heres-how-to-launch-google-voice-search.html#!/2012/07/heres-how-to-launch-google-voice-search.html
This link has seven steps, make sure S Voice is set to Lauch by double pressing home before doing step 1.
Here is a way to to access google voice search directly by double clicking the home button. (I didn't see that this had already been posted).
http://sgs3mod.blogspot.com/2012/07/heres-how-to-launch-google-voice-search.html#!/2012/07/heres-how-to-launch-google-voice-search.html
This link has seven steps, make sure S Voice is set to Lauch by double pressing home before doing step 1.