I answer all the time. My HMO always calls from unknown or blocked numbers. And because of HIPPA they can’t leave a voicemail detailing the reason for the call (I’m not sure if I should be upset at HHS or the FCC here.)
They probably can. But it’s an HMO with thousands of doctors and a non-deterministic phone tree. I don’t even know if staff know what phone number they’re calling from.