I agree- calls need not be made while riding a bike. Granted, people seem to concentrate on the road more when they can keep their hands on the wheel (and now on the handle bars) using hands-free sets, but it is still a dangerous idea.
Besides, if the voice clarity is anything like a Chatterbox, people will not like talking to someone on his or her way to the office doing 70 and 80mph on the freeway.
The main criteria for helmets (and all riding gear) are protection, comfort, and style. I'm pretty sure Bluetooth technology won't enhance any of those. My two cents.