If there's lore about how exactly they work I've long forgotten it (Wanted! was so long ago). However, I can tell you the way I usually treat them; around me, they've been used very similarly to radio signals. (Disclaimer: nothing beyond this line is canon fact, it's just what happens in my experience.)
Not unlike walky-talkies, they can be used to communicate in private between two people or to send a message out to whole groups at once. I treat them as if they have millions of possible frequencies and you can pick just about any frequency to talk to, and any other commorbs that are on, in range, and attuned to that frequency can recieve your message. So, say, a military unit might all set their commorbs to one frequency so that they can freely and quickly communicate with each other, whereas a shop owner or individual might find an obscure frequency that seems quiet and unusued and choose it like a phone number, "you can reach me on this frequency."