Calls

For iPhone 6, it is pretty straightforward:

Open Settings ➔ Phone ➔ Silence Unknown Callers and then set that switch to ON.

Other cellular phone makes and models… unknown, but prolly similar.

[edit] Oh! Forgot to remind you, Your approved caller list is your contacts list.

I am a dinosaur. I still have a flip phone.

Good advice but I cannot justify buying something I will seldom use.

Can a unique program be written for my PC to filter my land-line or flip phone?

I would probably have to route my phones through my PC, but that is ok.

Any ideas?

This is an entirely different kettle of fish.

Your existing cell phone, does it not have an option similar to the feature of the iPhone?

If the phone feature is not available, this request as clarified is likely to be in the category of ‘With enough money, time, and effort, just about anything can be accomplished’. I would think these three resources might well be quantifiable with four digits.

Communication technology evolves at an eye watering rate. As new tech goes mainstream, I have seen earlier tech (talking about your existing cell phone here) being disincluded in backward compatibility.

What I have done is place a tone from a wrong number at the front of my greeting. This tone will repel many computer generated calls, but not all. I also have a call blocker that will not ring for any number that I previously blocked. This prevents repeat spam calls from same number, but there is an infinite set of numbers they can call from, so it never ends.

The government "Do not call list" is a joke. It does nothing.

I wonder how much tax $$ we are paying for that?

Doh! I wonder if Google knows!

A search string “reject unknown callers” has yielded many promising results.

https://duckduckgo.com/?q=reject+unknown+caller&t=iphone&ia=web

You will probably get a more filtered list if you add your phone model to the search string. If your device is old enough that it is no longer supported, then it is quite possible none of these will help.

Android phones have a call blocker function as well.

Not what you are asking for, but there was an APCUG (computer users groups) video months ago showing how someone recorded and made part of their phone message the 3 telephone company tones that tell the caller that your phone number has been disconnected. Legitimate callers can ignore this and leave a message. This soon cut down his incoming calls!

This (as well as the similar solution already used by HTRN) is pretty clever, but will not accomplish the prime directive: stop the unknown callers from ringing the phone in the first place.

This would probably be worth the effort to try, no dollars, a little bit of effort and time, might very well help in the long run, easy to undo if you don’t see desired results.

That is what I have recorded at the preamble to my greeting. As I said, it repels some calls, but not all.

There will be a learning curve for incoming calls. They have to call once to find out you're disconnected or they have reached a wrong number

Someone is making money on the calls .A law with teeth would stop it. Make every violator pay each victim a penalty, like $5 or so and it would stop. Failure to pay would be considered a violation of a court order.