I'd love it if my cell phone auto-screened calls from numbers not in my address book. Give them a special message that explains the only way they'll get through is to leave a message. Or that they can register their number in a public registry that fully explains who they are and then I can decide whether to take calls from that number.
I never answer calls, ever. My voicemail suggests sending me an email. If the caller doesn't, it's like it never happened. The only reason I even have a SIM card is for data/tethering.
"But you won't be able to receive calls!", the salesperson objected.
"Perfect."