I’m healthcare and this is a HUGE problem for the service I work in, with people not answering. We’re not allowed to leave a voicemail for privacy reasons. Our organization phones dial out as “unknown” and our work phones HAVE to be on private number (sometimes shows as withheld). I have a system I can text off but it’s time consuming and doesn’t always reach patients. Our service has a wait list so often people are not expecting our call. But if it’s a call to follow up on a letter based appointment or a missed appointment - our policy is to attempt contact a few times then remove from the waitlist.
Personally knowing this, and having kids under some complex care teams, I always advise people answer and can always hang up.
As others have said above, people calling me to “upsell” now nearly all used display numbers.