This is the story I was referring to.
From what I saw, briefly, your post concerned handsfree devices, not headphones. I was answering a quote regarding headphones, which
is illegal by car or bike.
Here is the appropriate VC as well. Note it must be both ears in order to be illegal; most handsfree devices would be exempt.
Originally Posted by DMV
27400. A person operating a motor vehicle or bicycle may not wear a headset covering, or earplugs in, both ears. This prohibition does not apply to any of the following:
(a) A person operating authorized emergency vehicles, as defined in Section 165.
(b) A person engaged in the operation of either special construction equipment or equipment for use in the maintenance of any highway.
(c) A person engaged in the operation of refuse collection equipment who is wearing a safety headset or safety earplugs.
(d) A person wearing personal hearing protectors in the form of earplugs or molds that are specifically designed to attenuate injurious noise levels. The plugs or molds shall be designed in a manner so as to not inhibit the wearer's ability to hear a siren or horn from an emergency vehicle or a horn from another motor vehicle.
(e) A person using a prosthetic device that aids the hard of hearing.
Amended Sec. 45, Ch. 594, Stats. 2003. Effective January 1, 2004.