Here in India, SMS is almost dead already. WhatsApp comes pretty close to being in that middle overlap here, and has largely replaced SMS. SMS took off in the

Here in India, SMS is almost dead already. WhatsApp comes pretty close to being in that middle overlap here, and has largely replaced SMS. SMS took off in the years when networks stopped charging for them, at least up to a reasonable number of messages. After a few years of that, they regressed back into charging for individual messages, around the same time as when mobile Internet became cheap and accessible making WhatsApp a viable alternate. So now, most people I know use SMS only for OTPs and for messages from their banks and govt services, while personal communication is almost entirely through WhatsApp (and growingly, Telegram). I suppose a missing circle here is "Free of marginal cost", and being inside or outside of that circle matters to a lot of people.