Well, there is the underlying tension between the interest of the caller, who wishes to be heard immediately, and the receiver, who will have to drop everything

Well, there is the underlying tension between the interest of the caller, who wishes to be heard immediately, and the receiver, who will have to drop everything to pay attention to the caller. In a sense, email is more respectful of people's attention by being something they have to check in their own time, although notifications have spoiled that.