I like AlanBs call flow. It is similar to one that I use. Very effective against unknown robocallers and even many telemarketers staffed by people who are told not to negotiate phone trees or who may not even have a keypad.
In Anveo, the contacts list is the key. If you have a number in the contacts list as friend, family or business, they will ring right through. Real people trying to talk to you don't seem to have a problem pressing the right key. Once they have called (even if the call did not get through because of the test), you can create a new contacts entry by clicking the diskette icon in the Calls Received list, as well as in the Phone Book section. I do that for repeat spam numbers to give a text entry in the list. I don't use CNAM lookup, but numbers in the list do not do CNAM lookups even if you have selected to do CNAM lookups. I look up numbers that did not make it in 800notes. It is surprising how many numbers hit there.
I know the above discussion mostly isn't voicemail... for that, make changes by clicking the pencil icon in the Voicemail element, and set the message and timing that you want.
There are fancier things you could do. You could, for example, have only family calls transfer to your cell phone if your home electricity is off.