title: How to use Android device as a bluetooth headset for another mobile phone?
body: <p>I want to make my android device working as a bluetooth headset.
  I search the Android APIs, but I just find some interface which
  can make Android device working as a masters, not as a device(bluetooth headset).
  I'm also ready to modify the source codes of Android OS, and rebuild the OS.
  What I hope is, when Android devices connect to a mobile phone with bluetooth, the Android devices can work as a bluetooth headset.
  I don't know whether there are interfaces can do this, or I should modify the Android OS?
  Thank you!</p>