title: Detect headset button click on iPhone SDK
body: <p>Is there a way to detect the headset's play/pause button click?</p>
  
  <p>I managed to detect the volume buttons clicks using:</p>
  
  <pre><code>AudioSessionAddPropertyListener( kAudioSessionProperty_CurrentHardwareOutputVolume , audioVolumeChangeListenerCallback, self );
  </code></pre>
  
  <p>But I can't find an AudioSessionProperty for the center button. What's the way to do that?</p>