We've seen a few bone-conduction devices before, including a mobile phone, a sports headband and an industrial safety helmet, but this is definitely the first we've come across that sends the good vibes by Bluetooth.
As with other bone-conduction gear, the point of the Sound Leaf is to circumvent the outer ear and deliver the vibrations that sound is made of from the phone, through the bones of the skull and thence to the inner ear. Apparently, it's useful in noisy environments like building sites or Tesco on Christmas Eve.
The new 45g model runs on two AAA batteries for about 15 hours a pop and has a flip for taking and ending calls that has a microphone on the end. DoCoMo has thoughtfully engineered in a softer vibration pad so as not to jiggle the bones of the cranium excessively and the whole thing even vibrates in your pocket when a call arrives - who would've guessed it?