Someone just sent me a link to this site. Looks legit, plus it's ".gov" and I am sure I have heard of it before. Anyway, you should check it out cause telemarketers need to be stopped. Plus, I only have a cell phone so I basically get charged (via minutes) for incoming calls which I have not requested which is totally lame!
The National Do Not Call Registry gives you a choice about whether to receive telemarketing calls at home. Most telemarketers should not call your number once it has been on the registry for 31 days. If they do, you can file a complaint at this Website. You can register your home or mobile phone for free. Your registration will be effective for five years.
Anyway, check it out: http://www.donotcall.gov/