I remember in the 90's, when living in LA, hearing stories about scammers targeting elderly people on the phone for money. Apparently they were calling from what were known as "Nevada boiler rooms" - something to do with the laws there making it easier for them to escape prosecution.

Eventually we started getting calls where I lived and at the time I was between contracts and at home a lot so I would engage the callers in conversation, pretending to be somewhat dumb, to string them along for about 20-30 minutes. At the end I would just bluntly say "I know your call is a scam but I've just stopped you from targeting several other vulnerable people". And then I'd hang up. They stopped calling after a while.

Recently I've been getting calls from the Nigerian computer scammers pretending to be from Microsoft saying there is a problem on my computer and they want passwords etc for remote access, (this has been well publicized here in NZ). I either do the above or better still because I don't get a lot of calls normally on my landline, if I suspect it might be a scammer, when I pick up the phone I'll say "Good Morning, Microsoft New Zealand, How may I direct your call" The response is usually a moment's stunned silence then a hang up.