BMW already make a Bluetooth enabled helmet - although it is a bit pricey.
I believe Dick Smith, Tandy, Radio Shack and similar stores also stock the necessary bit and pieces to 'retro' fit an existing helmet with Bluetooth technology...and it's not as pricey as the BMW helmet.
Even thought I answered yes to the question, it's not on top of my 'must buy' list, in fact it's way way down the bottom of the list...