This is terrible especially when you're applying for jobs. All calls from unknown numbers have to be answered because you never know who's calling you back.
I did miss a few calls when recruiters called me without scheduling it first. I made it clear they needed to email me first with a call time, or I wouldn't be reachable. Sad, but that's how terrible the spam problem is on phones these days.
Blocking rings doesn't block voice mails, right?