I recently encountered a young woman ( I won't say lady) who was using her mobile whilst driving, I gestured to her with my thumb in ear & little finger to mouth ( demonstrating using a 'phone) & shook my head. This is the answer I got. http://tinypic.com/r/j8dw7c/5
I take on board what you are saying about deaf people, but by the same token they can't hear music so they are more likely to concentrate on their surroundings, but to have the music plugged directly into the ear I feel it could affect concentration, I will give it a go but I do not really fancy it