Apps keep closing and Voice Control Keeps Popping up on iPhone 3GS?

I recently got an iPhone 3GS and the Voice control keeps popping up for NO REASON! How can I permanently disable it unless I turn it on. Also, I can be through half way through a text or on a game and it will exit onto the home screen without me doing anything and sometimes when it exits an app, it will make the home screen go grey and the essential bar (at the bottom) is the only highlighted area!

That's a result of the home button going bad. You need to replace the module, go to a apple store. It should be pretty cheap.