S Voice for Galaxy S III may look and work a lot like Siri for iPhone 4S, but it has been shown in multiple tests that both voice-based services are, in most ways, inferior to Google Now that comes built-in with Android 4.1 Jelly Bean.
Galaxy S III owners get no choice between S Voice or Google Now (they might when it gets updated to Jelly Bean in October), but Galaxy S III owners who are rooted can replace all S Voice functionality in their phone with Google Now in a few simple steps. Check out how after the jump.
All files to be downloaded during the following of this guide can be found in the official thread.
This guide assumes that you are using the stock TouchWiz Android 4.0.4 ICS ROM on your rooted Galaxy S III, and that you have ClockworkMod Recovery flashed. Note that the developer has only tried this on an AT&T Galaxy S III, but it should work on all other Galaxy S IIIs as long as you are using the stock ROM.
Step 1: Download Google Now .zip file. Transfer it to directly under /sdcard on your S III.
Step 2: Reboot into ClockworkMod (CWM) Recovery Mode. You can do this by shutting down your S III, and then pressing and holding Volume Up + Home + Power buttons until you enter CWM.
Step 3: Navigate to install zip from sdcard > choose zip from sdcard > [file you transferred in Step 1] to flash Google Now to your S III.
Step 4: Select reboot system now from CWM’s main menu.
Verify if Google Now is installed by looking for an app named Google in your apps drawer.
Step 5: Install and set up Google Latitude on your Android device.
Step 6: Launch and completely set up Google Now from the icon in Step 4.
Step 7: Go into the settings for S Voice and deselect Launch S Voice.
Step 8: Install home2 shortcut from Google Play.
Step 9: Press your S III’s home button twice and select Voice Search to launch Google Now. It should display a blue microphone. Follow on-screen instructions.
Step 10: Launch Google Now once again from the icon in Step 4. Press the menu button and tap Refresh.
Step 11: Reboot your phone.
If you followed the steps correctly, your Samsung Galaxy S III on Android 4.0.4 ICS with TouchWiz will now exclusively use Google Now instead of S Voice. For queries, please visit the official thread linked above Step 1.