Probably phone operators were not impacted too: SMSes bundled with flat plans are still flat plans and Europe style unlimited calls + 100 SMS per month plans are still there and those SMSes are still mostly unused.
So we could have a killer app and yet nothing changes in the flow of money around it.
UX wise, WhatsApp is a big improvement over SMS. Vocal messages, I'm not a fan of them. A waste of my time.