In order for this to work, you need lots of people to start doing it, but I think it's awesome. When someone calls, you say "Oh, hang on, I'm really interested, but there's someone at the door (for example)." Then, you put down the phone without hanging up and walk away. They wait 1-2 minutes before they give up and hang up. Their costs rise, because they spend more unsuccessful time on the phone per customer. Meanwhile, you don't waste time talking to them. If enough people did this, it would become expensive even for telemarketers in India to make it worth the while. And when your phone beeps with the "off-the-hook" signal in a few minutes, you hang up.

I love the idea, though I do understand it's hard to operationalize.