I never found a good solution for this problem, so I'd like to raise this question again.
To recap, I'm looking for a way to suppress all calls that don't come from a number in my contacts list. The advice I received was:
1) Use the built in "Interception Rules", which includes exactly the feature I'm looking for. Sadly, my version of Android doesn't have "Interception Rules".
2) Install a custom ROM with better call-blocking features. I looked into this, but decided it was too complicated for me.
3) Use "Mr Number", a 3rd-party app. This is the solution I ended up using.
Mr Number never quite worked. Calls from strangers would ring once before geting suppressed. (I would prefer that the phone not ring at all for calls from strangers.) Today, Mr Number completely stopped working. (I think they've discontinued the free version, because when I look at Mr Number, all I see is a menu of fee-based services.)
So, I'm asking once again: Does anyone know of an easy way to suppress calls from strangers? Do you guys know of any app other than Mr Number which offers this feature? If you have "Interception Rules" among your settings, is there some trick to enabling those settings? Are "Interception Rules" specific to a niche version Android, and if so, can you tell me what version that is?
-TC