A few more tips about telemarketers:

Don't hang up on them without hearing their pitch. Most telemarketers will count that as a "no answer" and you'll end up on the call back list. You can be called back 10-20 times like this. It's always best to hear what it is they're selling (it'll be in the first 30 secs of the call), then politely request to be taken off the calling list.

Even if you are taken off the calling list for that product, you may be on other lists. Ask for the product companies toll free number so that you can call and be removed from the master list.
If you are speaking to a telemarketer who is rude or continues to pitch after you've said 'no' three times, ask to speak to her/his supervisor. That'll prevent her from doing it again, and you'll probably be removed from the list.

Most importantly, DON'T BE RUDE...as tempting as it is, you're asking for trouble. If a telemarketer is having a really bad day (which isn't unusual) they may decide to put you on call back just to get even. No, that's not exactly legal, but it happens. Besides, a lot of telemarketers are not allowed to hang up on you, so they *have* to listen to you. No one deserves to listen to abuse just for doing their job.
Always remember that the person on the other end of the line *is* a person. If you want to know how to arrange it so they never call you again, they can help you do that.
ceitagh
(former telemarketer)