I'm on PA's no-call list and am surprised at how effective it is-- we almost never get telemarketers anymore.
When I was at my previous residence and got calls from phone company marketers I'd try to get them with the classic "I'm sorry, but I don't have a phone" line (I believe Sienfeld deserves credit for this one).
Amazingly enough it worked about 1 of every three times-- they'd say "Oh, sorry, and hang up" And even when it didn't work they'd usually laugh and not go through any more of their anti-rejection scripts.
Try it, it's fun!
Scott