The calling is done by a pre-programmed computer. The nasty little human who answers the phone at the scamming place has no idea who they have contacted.
They are usually off shore where our laws are not enforceable. It's best not to engage them. They know they are unlawful, and sometimes are phishing for your personal information.
They DO make such a device, and I just ordered one!
http://www.amazon.com/gp/product/B004BTVQ5E?psc=1&redirect=true&ref_=oh_aui_detailpage_o00_s00
$50 is a cheap price to pay for piece of mind.