How to send unknown callers directly to voicemail on iPhone (while allowing text and know callers through)
Thus far, an app called WideProtect seems to do what I want.  It allows you to block numbers per area code while still white-listing numbers in your contacts.  It's a bit annoying as

You can't just block out +1 (xxx)-xxx-xxxx, but most spam calls come from just a few area codes for me

You have to go into the app and have it re-whitelist every time you add or remove contacts.  A bit annoying, but I've received 20 robo-calls in a day, so probably worth the hassle.


Blocking just my area code dropped my daily robo-call count from 20 or more to 2-3.  Slowly adding area codes as I get robo-calls from them.  Was able to put my ringer back on.
PS: WideProtect can only block 40 million phone numbers.  This sounds like a lot, but when I'm trying to block every number except ones in my contact list it runs out of space fast.  Still happy with the product, but won't block everything out of the box.
NOTE: Apple has added &quot;Silence Unkown Calls&quot; which makes this moot