The FTC do not call registry does work and it works well. I signed up for it a couple of years ago and after a couple of months I quit recieving any calls.
It will not stop charities and companies you "have business" with from calling you tho', you're gas card company might bug the shit out of you trying to get you to buy life insurance and you can't stop them....
As for autodialers; they're the standard of the industry, if they didn't use them they wouldn't be able to create the volume of calls needed to turn a profit, I wouldn't bet on recieving too many "in person" sales calls on your cell phone....