On Thu, 2019-12-19 at 11:02 -0800, William Herrin wrote:
I call your phone number. Your phone company compares my number against your whitelist. Ring through on match. If no match, "You have reached Name. Press 2 to leave a message. Press 3 to enter your code. Press 0 or stay on the line for an operator." Ring through on a valid code. If 0, the call connects to a call center where a live operator evaluates the call. Who am I? Why am I calling? Do I meet the plain-English criteria you've established for calls to allow through? If no, the operator offers to connect me to your voicemail. If yes, the operator dials you, explains who's calling and asks your permission to connect the call.
It really doesn't (currently at least -- until robocallers start using voice recognition to defeat my system) need to be this complicated or over-engineered. A simple audio captcha works wonders. Hello. If you are a telemarketer, press 1. If you want to speak to somebody at this number, press 5. Anyone pressing 1 gets their caller-id added to my blacklist and is asked to add our number to their do not call list. In reality all telemarketers use robocallers so they don't even get that far. Anyone pressing 5 rings through (with additional processing described below). But that's it. That has blocked 100% of robocalling from actually ringing the phones in our house for the last few years. I couple the captch greeting system with a whiltelist (i.e. only callers not on the whitelist get the above prompt -- callers on the whitelist ring through directly with no greeting). One gets on the whitelist because (a) I add them explicitly, (b) their number was called from our house phones (i.e. the PBX automatically adds all outgoing numbers to the whitelist) (c) they pressed 5 at the prompt. The result of that last one (c) is that people only ever hear that prompt once and if they press 5, they never hear it again. Unless of course I remove them from the whitelist. That has never had to be done to the best of my recollection. Of course I cannot know how many legitimate (robo)calls have not made it through the gauntlet, but I also have not had anyone complain about not being able to reach me. I figure if it's really important, some human from wherever the failed legitimate robocall is coming from will eventually get in touch with me. I do also get notified when a (i.e. a robo)caller doesn't choose either 1 or 5 and have noticed the very odd robocall that I would have liked to have received (very few and far between -- maybe 1 or 2 a year), and add them to the whitelist which works well since failed robocalls typically get retried so I get it the next time around. One might argue that having to deal with the notification on each failed robocall washes out the value of the system, but I would argue that reading a text message about a failed robocall, when I feel like reading it, is a more than fair trade-off for not having to interrupt what I am doing to answer the phone and get frustrated at another phishing/scam/etc. attempt, and it gives me peace of mind that I will catch (the very very few) failed robocalls that I did want. b.