Some would prefer Google Now over S-Voice since it's better at handling voice recognition. This will make it so Google Now is used instead of S-Voice when activating thorough headphones on the SIII, S4, Note II & Note 3.

Here's how to do it:
  1. Settings
  2. more tab
  3. Application Manager
  4. swipe over to select All
  5. click S Voice
  6. click Force stop
  7. click Disable
  8. Google Now will take the place of S-Voice

See More: Replace S-Voice on the Galaxy SIII, S4, Note II & Note 3 with Google Now