bone-conduction, headphones. The idea is that sound vibrates into the skull and then straight on to the auditory nerve; though if someone is blasting their iPod next to you on the train ride home, it would seem your auditory nerve is going to be getting a lot more noise than signal. Plus, constantly pressing buttons situated very near to your cerebellum and brain stem can't be a good idea, either. But we'll defer to the authorities on this one.
Read - NVP200
Read - NVP100