I happened because the phone operators made SMS a paid feature, while Whatsapp over wifi was free. Then the people for whom SMS was not free started using Whatsapp (or Messenger or other apps) and eventually those who used to use SMS switched to the same apps because their contacts were using them.

In some places the switch to these apps took longer (like France, because SMS had been free for a long time) but there is a fundamental asymmetry since SMS is free only for part of the users (so the others will never use it) while the apps are free for everyone. In the end, everyone ends up mostly using these apps.

From my experience in France at least, nobody relies on SMS anymore and less and less people on regular calls, it all goes through Whatsapp.

Even I am guilty of that for both SMS and calls, having a single featureful app with contacts ordered by the most recent discussions descending (as in my country SMS is largely replaced by Whatsapp) leads to less friction than having to scroll through my actual phone's contact.

I can answer this! The moment that one tenant in my house didn't have an iPhone, so couldn't be in the house group chat on iMessage. It would take too many calls to coordinate the six people we have at home. Group messaging is the best option, and of those, WhatsApp is the best option.

Around the time smartphone and widespread data coverage made it feasible. It, and other services like it, offered a clearly superior experience to SMS/MMS, and RCS arrived way, way too late. As for why a particular service succeeded in a particular market, I imagine it all comes down to marketing, luck, and network effects. WhatsApp is probably not my ideal service (mostly because it uses somewhat device-tied accounts) but it's what 90% of people use

Almost all phone calls I receive are "actual" phone calls though. And SMS still gets plenty of use as the lowest common denominator for new recipients, but in practice over 95% of my received SMS are from computers now