There was a thread in April about the recent plague of robotic telemarketing and scam calls. Sketchy charities, scam threats of legal action, false claims to be returning your call about some product on TV, etc. To address this issue on our home phone, I have been using this new service called NoMoRobo which blocks most such telemarketing robocalls:

http://nomorobo.com

It works on most digital voice systems such as from fiber and cable companies, and some VoIP services, but not on standard non-digital service. The telcos would not cooperate with them, presumably because the telcos make a lot of money from robocallers, so NoMoRobo uses the simultaneous ring feature that most digital voice services have, where you can have them ring another number like your cell phone at the same time as your home phone. NoMoRobo will provide you with a special number to add to your simultaneous ring list on your telco website. After the first ring, NoMoRobo screens the caller ID info against over 850,000 telemarketer numbers in their database. If they get a match, you don't get any more rings on your home phone after the first one. (If the telcos would cooperate with them, they could suppress even the first ring. But there are devices you can buy that will do that. Search Amazon for "call blocker" and look for ones that have first ring suppression capability.)

NoMoRobo makes money be charging commercial customers for their service, but it is free for consumers. Part of the registration process, which the website will guide you through, involves NoMoRobo making one test phone call to your home phone so they can verify that you have signed up properly and they are receiving your caller ID information.

Some people may be leery of a company simultaneously receiving all their phone calls. But of course, the telcos and the NSA are already doing that. NoMoRobo is a relatively small operation, and I think their computers would have their hands full just screening the caller IDs for their 190,000 subscribers. Eavesdropping on any answered calls is likely beyond their capability, even if they had any inclination to do so. But use your own judgement.