Completely Replace S-Voice with Google Now on Samsung Galaxy S III
When you buy any of Samsung’s newer devices, you have a choice to make. If you stick with stock firmware, you can use either S-Voice or you can go with Google Now. However, when using Google Now, you may still find that S-Voice is still around doing things even when you don’t want it to. Now, there’s a way to get Google Now running and turn S-Voice off for good.
The method was posted by XDA Senior Member Ghstudent. Despite being released for the AT&T Samsung Galaxy S III, it should be compatible with all Galaxy S III devices and possibly even non-Galaxy S III devices with S-Voice in their ROMs.
It is a pretty easy method to use. Users will need to be rooted, of course. From there, it is a three step process where users install Google Now, activate it, and then replace all instances where S-Voice is used with Google Now. Users will need at least a root manager application and home2 shortcut, which helps remap the home button so that a double click will launch Google Now. Once completed, users should have a number of ways to get to Google Now and should be able to avoid S-Voice.
For more details, go to the original thread.