re: Calling one specific person and it goes to voicemail

Some carriers filter numbers that aren't in the receivers contacts. Also, you can do this on iOS by ignoring unknown numbers. And then you have apps like Robokiller which also block calls that are risky. And as someone else mentioned, the equivalent of Do Not Disturb.

Then, you have the fantastic possibility that you're dealing with someone old school like me, that doesn't believe that just because a phone is ringing, it needs to be picked up. I called an old friend, he rolled me to voicemail. He was in therapy with his kid. Another was on a conference call. No big deal. Just don't actually leave a voicemail. Ever.