Had someone ask me why their phone didnt make noise or vibrate when they recieved calls the other day. They were pressing the volume down button with the unlock button to get the screen to turn on/off. So it would slowly mute the phone and take the vibrate off once muted.

They would have benefited from the buttons not being less than half an inch away, and possibly on the opposite side. (Not sure what kind of phone it was, it was a cheaper device it seemed.)