I know exactly which setting you're looking for, and I can show you where it's at. If your Voice Commands prompt is coming up on the phone when you press the home key twice, that's the default setting on the phone. The good news is that it can be changed on most phones. Go to settings> applications> click double tap home key> then either select an application of your choosing or choose none as an option.
Let me know if that's what you're looking for, and if that worked for you.