I've been doing something like this for years with Asterisk. When people call and I don't recognise their number, I ask them to enter a random 3 digit code to c

I've been doing something like this for years with Asterisk. When people call and I don't recognise their number, I ask them to enter a random 3 digit code to complete the call. This is highly effective at getting rid of telemarketers and political robocalls because the system they use does not connect a real human on their end until you speak. By the time the human is connected, they missed the 3 digit code, and the call is dumped after a timeout.