Whenever someone sends me an important message and I don't read/respond in time, they call to get my attention so I can do so. My ex used to get mad at me for "ignoring" her for 2h or more and would call. I was just busy doing whatever and ignoring the phone as usual.
I hate that. Also in a business setting. By definition a message (be it text, email, whatever) is not urgent. They might be important and of course you shouldn't leave them unread for days, but for urgency there's calls.