Buy a Twilio number that forwards to your real number. Then whoever has that number can call it, and it will ring you from the known Twilio number. Add to address book and voila!
I assume the spammers buy "known active real person phone numbers" from somewhere (probably the awful carriers themselves), so it might be less likely for them to find a new Twilio number. But as soon as you give the phone number to some company that sells (or accidentally leaks) their customer data, that number will be burned too.
I don't know about calls, but I definitely get spam SMSes on my persistent Twilio SMS numbers.
This is a simple and neat idea. I'll try it on the weekend.