Face accidentally presses mute or speaker phone

Often when I'm talking on the iphone4, my face hits the speaker phone or mute button. This is very annoying especially when I'm talking and wonder why the other person keeps talking without answering me. Then I remember that my face probably hit the mute button. Is there a way to make this screen go away or an app even that disables the buttons on it while talking on the phone?

Thanks,

Dirch75