And is rarely enforced. I see people drive with ibuds and the like constantly, and cops won't do anything because they're not sure if it's just a hands free set or not. The only time one would get caught for it is when there's an accident.
Regardless of whether it is enforced or not, I'd rather drive on safer roads. But there's far bigger issues to deal with to increase road safety before we start dealing with people wearing headphones etc so I don't really mind as much.
Still, provided they can still hear important traffic sounds, I don't have a problem if they keep an eye on the road unlike texters.