I dunno' about the effectiveness / efficiency of a 'do-not-call' list especially when run by the US Govt. However, I do know a technique I've been using for about a year and a half seems to be quite effective.
When I get a call from an unwanted telemarketer (anyone ever get a
wanted TM call?
), I tell them I've been waiting for someone to call me about their product and ask them to hold for a moment while I get a pen. I set the phone down, go do what I was originally doing, and come back in about 20 minutes. If they're still there (only 1 ever has been), I tell them I'm having a hard time finding a pen and would they hold a few more minutes. Rinse and repeat!
My TM calls have been reduced drastically since I started that so the TM'ers must have some kind of list to begin with....