I think straight calling someone on a chat program is rude because it unnecessarily breaks flow. I have to connect my Bluetooth headphones so I can hear you from the start, but that takes a couple seconds. If I'm not quick you'll stop calling before I'm ready, and it happens frighteningly often that people don't answer when calling back immediately, so you'll break my flow a second time.

Usually, 15-30 seconds are enough for me to mentally "put away" whatever I'm working on, which allows me to quickly resume once we're done. Often I write a comment describing what my last thoughts were. That can sometimes save a good 5 minutes or more.

At worst I'll say "give me 5 minutes" or "if not important, does 14:30 work?", but that's because I'm deep in thought and it will take a long time to get back to where I am.

I didn't say I get mad that he calls without asking. My comment was about the "please call me back" - that message could have been the question. It's the same as "hi"

You can choose to answer the call or not

.. and either way, my concentration is broken for (what researchers keep saying is) 30+ minutes.

Nah. I'm not in the mood to speak to THAT asshole after he wrecked my morning.

In the middle of a text chat, you say "call me and share your screen" and then we 'go voice'. Calling without warning, now, and without justification (visible flames or blood, timely health risks, massive outages), is like dropping by your cousin's house out of the blue for a week.