EDIT: It's not only what everyone has (WeChat in China), instead of just many people (WhatsApp in EU). It's also the default payment service, you pay through it all the time in all kinds of situations. It's like WhatsApp but more monopolistic combined with PayPal but also more monopolistic. And both with full government support so no worries some bank lobby gets in you way.
iMessage? (US)
WhatsApp? (EU)