Would a simple solution, like demanding that anyone who isn't in your contact list pay a relatively substantial amount (like $5, or even $0.5), in order to contact you, and you are the one that decides if to return that money when the call ends or to keep it for yourself (send it to a charity/pay taxes).

This would also cripple a lot of business in advertising, but not a big loss, if someone really wants to talk to you, they can pay the price.

What am I missing? Why would this not work? What side effects on other industries could there be?