The moment you realise you're talking to a telemarketer stop them and ask them thier name, which company they work for, and the address of the company. When/If they have told you, say that they are welcome to continue with their sales pitch but that you are now recording this conversation, your time is charged at $50 per minute or part thereof, with no guarantees of a sale, and that any continued conversation from them will be taken as acceptance of these terms. Then ask them to confirm the name, address etc they have just given you before allowing them to continue.
I've used this several times now, and the normal response is "click...brrrrr" or "are you serious?" to which I answer "yes".
I've never had anyone continue. Shame really, I wanna see what happens if I try billing them for my time
