I'm on the do-not-call, but another great help is the Tele-Zapper. Any automated calls, it'll kick your # out of their system.
I got mine years before the DNC. You just plug your phone jack into it, and that into your wall jack and you still get calls for a few days. But after that, almost none.
Now that nearly all those calls are automated, you can imagine how few I get.
I don't even need to leave it on all the time - I'll have to hook it up soon with the political stuff heating up though.