My phone uses BT True Call and asks the caller to give their name. Only then does it ring and replay the reply that they give and offers me a choice of accept the call, not accept or block permanently. For numbers recorded in my phones contacts list, these calls come straight through. While I have a particular BT phone though not using a BT service, you can have this arrangement with any phone if you use BT (presumable have to pay extra). Initially, we found that calls from the NHS or Doctors were not coming through as they abandoned the call but they seem to be used to this now and do go through the system. Most spammers or commercial sales abandon the call. We can see such abandoned calls in the list and I will sometimes check them out. If they are dodgy, I block them but occasionally we may spot a genuine caller who did not get through.
Dave