YES! This is exactly the right approach! If everyone did this, it would put an end to telemarketing overnight. When people just hang up the phone, it takes up 5 seconds of the telemarketers time. When you just put the phone down, or keep them on the line, it takes up much more. This is time that they are not calling someone else. If everyone did this, so much of their time would be consumed, without making sales, that it would put them out of business!