“Cynaps (derived from ‘synapse’) is the world’s first bluetooth enabled, bone conduction headset, discreetly installed into an easy to wear hat. No earphones are required.  Just wear your hat, and the sound from your phone or PC is conducted directly into your inner ear through vibration.  You can listen to music or have a phone or Skype (for PC & Mac) conversation, even while doing an activity that requires your ears, eyes and hands to be available.”

http://www.maxvirtual.com/

http://www.youtube.com/watch?v=9y-k_NaG1Z0&feature=player_detailpage