A European advertising firm may have crossed the line by experimenting with a dynamic that uses a commuter's head rest, often the train window, as an advertising platform.
Is bone conduction how you'll take a phone call with Google Glass? It could happen.
This prototype cellphone, from KDDI Labs and Kyocera, doesn't have a speaker. It doesn't need one. Put it up against your head and it sounds just like a regular phone with a speaker in it, and if you happen to be wearing industrial ear protection, it'll work perfectly straight through that, too.