Like many people, I don't wish to receive unsolicited phone calls/texts/emails from people who are trying to sell me something or scam me.
I am aware of passive ways of dealing with the problem but I am asking here for ideas for actively discouraging such calls.
I want to discourage the same people from calling me twice.
I want to discourage them from calling other people. In other words I want to stop cold-calling altogether. I believe it has no useful place in the modern world.
I am looking for novel ways of causing the maximum inconvenience and expense to these annoying people. Of course I am only interested in law-abiding methods.
If possible I would like the methods to be scaleable to the status of a campaign.
To repeat, I'm aware of passive solutions but I want ideas for active solutions that will hit these people hardest and preferably in their wallets.
Thanks.
EDIT
I'm very grateful for the answers so far. However they are very low-level solutions. I realise I wasn't clear enough. It is easy enough to annoy the grunts on the front line and anyway they are used to it. I am looking for ways to inconvenience the decision makers at the highest possible level.
Hello! This is the [city] Police Department, how may we help you?
Probably more of a good story than advice.