A lot, if you’re apple.
The iPhone ships with a mic on the earphone cord which is clickable and can do all of the following (in addition to being a microphone):
6 actions from a single button. I’ve seen other smart phones (e.g. the dopod) actually have 6 separate buttons for these actions What a waste. Amazing. And I only discovered the 6th one today… I wonder if any more surprises await. Can it cook my breakfast?