Yes, absolutely a blanket block, provided the call went to voicemail. The number of "unknown" calls that are important versus robocall or such thing is for most of us probably like 1 in a 100. And of course, you should be be able to turn the feature on and off -- though admittedly being able to turn off features you don't want is not a strong suit of the iphone.
Ideally, you control the settings. Want all unknown calls to go to voicemail? Click YES. Want to turn that off if you have reason to believe Dr. Smith will be calling with your MRI tests from an unknown phone, or just because you want any of your doctors to call you at any time from unkown phones? click NO block, and leave it off forever if you like.
I'm not an engineer, but it seems like it should be doable to me.
Sure, I'm down for that. Again though, that's different than what I was originally saying. I understand now where you're coming from.