Tell them to contact the Direct Marketing Association.
Tell them to contact one of the three major credit companies and tell those companies not to give our information "for marketing purposes". Credit checks could be done when they want them done, but banks, etc aren't sold that information, etc.
Tell them the advantages of using modern answering machines which no longer use tapes that break.
They might decide to change to an unlisted number with call blocking as well (my phone company does not charge extra for call blocking provided you order it at the same time as ordering an unlisted number and use a voice mail service for their "public" number.
I use Voice Exchanage a voice mail service. It's excellent. For $10 a month it gives me a public phone number, an toll free one at that. And it pages my cell phone when anyone leaves a message, so I can go to any public phone and retrieve my messages. This is the number I give out to anyone and everyone. No, I'm not trying to avoid sales calls! I had to disconnect my phone to save money for awhile. But this way only a handful of friends or relatives will call my cell phone and I tell most of them it's mainly for emergencies.
Voice Exchange's number is: 800-600-6699. If you decide to use them, please give them my name: Seamus O'Hargadain pronounced: Shamus O'Hargadawn. I get some kind of discount if you do. And, I think you would if you send them someone. Excellent service, once in a great while there may be a system problem. They also offer Caller ID (it's verbal) for a small extra fee. And they can offer you numerous little extras such as