I believe that I made a BIG mistake when I finally lost my temper and told a spammer that we will never, never, never buy or use any of your products. Wow! After that I started to receive at least 4 times as many unwanted calls. I don't answer them any more. If "RoboKiller" answers the call, will that make them made and put you on other "call lists".
I have even received 3 calls that appeared as my own number!
Another thought: I believe that AT&T (and others) are encouraging these calls by allowing "call ID spoofing" at all. I used to be an AT&T technician and think that they have the ability to TURN OFF ALL SPOOFING in the Central Office. If they can't turn it off, at least charge $0.10. or less, for each ID spoof. That would allow legitimate users (doctors, schools, etc.) to get through, but would stop spammers.
Another thought: I saw a forum message that claimed that AT&T executives told him that there is a big push for customers to use "minutes". I have unlimited. Do many people still use "minutes? Anyway, robocalls that go to voicemail use "minutes" and a lot of them. 10 robocalls a day, about 2 minutes per day, times 30 days equals 60 minutes per month. If true, this is certainly evil and affects ALL users, because of the robocalls.
Another thought: If you have answered some of these calls, have you ever wondered why they first ask "Can you hear me"? When you answer "Yes", they somehow save and use your "Yes" answer to validate using your number, as in "Can we call you in the future?", "Yes". "Can we sell you number to call lists", "Yes". If this is true, it is extremely fraudulent, but, if outside the USA (see below), hard to prevent.
Last thought: The "DoNotCall" list is only good for spammers in the USA. The marketing spammers have created companies outside of the USA and are exempt from the DoNotCall list.