The FTC has set up a registry to block telemarketing calls. Sign up at DoNotCall.gov. The server might be slammed right now, though. Apparently they’re getting hundreds of registrations every minute. As of 5PM ET, they had 735,000 registrations. You can read more about the Do Not Call Registry at the FTC site.
You can also take steps to stop receiving junk mail at home: Junkbusters provides information and form letters to do this.
Another way to prevent telemarketing calls and junk mail is to send in those opt-out notices that your financial institutions provide. They often allow opt-outs by telephone, too. Credit card offers usually also provide a telephone number to opt-out of credit reporting agency spam lists. One phone call will take you off the lists of Experian, TransUnion, and the rest for two years. They’ll send you a form that you need to return if you want to make this permanent. So annoying, but worth it.
Now if I could only get the ACLU and ActForChange to stop sending me junk mail…