I'm in the US and I get an incredible amount of spam calls, as well as (before) calls from coworkers about non-urgent things.

I since just have my phone block all calls except those pre-made appointments on my Google calendar, and the number by which people can reach me changes depending on the scheduled hour, all programmed via Twilio.

I have a couple of whitelisted incoming numbers for family/SO and that's it. Everyone else has to make an appointment, or send me an email or instant message which I will usually see within a few hours. I generally tell people that email is the fastest and most reliable way to reach me.