Actually Apple has made this a point in their advertising (Seri will respond to voice commands) having the actor talk to his I-device and it responds.. Not just the Google app.
Google on my Droid has a microphone ICON, I tap it the keyboard goes away and it listens.. I tap again (or stop talking long enough) it blings and displays what It thinks I said (Usually right) then does it's search.
There is also a voice command app that displays (Typed) What do you want to do? I can tell it something like "Call Keith" and it will, or Check E-mail and it will, or things like that. Never used it though.