Unfortunately the "marketing" principles of telcos - at least our local ones - preclude them implementing proper processes as they want all calls to be answered in order to charge for them.
This obduracy represents a problem for people receiving nuisance calls. They can have a "caller ID" device (for which our telcos charge a monthly rental - about $5 - to enable the service) which will alert them to either the number causing the nuisance, or that the number is blocked, but the phone will still ring.
What should be provided, is a service such that a caller from a "blocked" number will not cause the phone to ring at all, but get a recorded message instructing them how to use a prefix to cause their number to be revealed.
Other problems include enterprises (notably hospitals and nursing homes) whose PABX systems fail to reveal the caller ID (not even showing it as the switchboard number) and public phones (though these are becoming "hen's teeth").
When "on call" I am expected to answer calls even if the caller ID is blocked, though on principle I do not identify myself when answering such calls until I have verified the caller.