I think of it this way: calling somebody is a very large demand on their time and their mental bandwidth. You're expecting them to drop everything and devote all their attention to you. This is very rarely justified if you're just exchanging simple information or making plans or the like.
It's pretty much only justified if you've got very urgent (I've been waiting outside for ten minutes, where are you?) or complex things to discuss (what are our plans for your mum's birthday?). Most of what you have to say, even to your friends and family, doesn't need to be immediately imposed on them in real time and can comfortably be relegated to low mental bandwidth, low time pressure media such as SMS.