Functionality of the iPhone Microphone button

The iPhone headset has a multitude of functionality. The obvious ones are listening to music, and using it as a hands-free device when talking on the phone. However, the microphone also has a built-in button, which can do a lot of things:
 

• When listening to music, watching a video etc.:
  • Single press: play/pause
  • Two quick presses: next song
• When receiving a call:
• Single press: accept the call
• Long press: Reject call (this will be confirmed by two distinct, low beeps)

 
If you receive a call while already on a call, you can accept or reject as above, and if on two calls at once, a single press will switch to the other call, while a long press will hang up the active call. Whenever you hang up a call, this will be confirmed by the previously mentioned beeps.