Extraordinary momentum for the IM client that's not BBM or iMessage.
Anyone close to mobile or youth trends knows that WhatsApp has stealthily become the client of choice for smartphone users that want to IM each other across different platforms.
How it's done this is something of a mystery given that there are many other products in the space and that WhatsApp has done virtually no marketing.
It also charges real money – $0.99 on iOS and $1.99 on some other channels.
But this may have been the masterstroke, and charging a fee has enabled the app to stay 'clean' and free of advertising, and mitigated against the need to sell user data.
WhatsApp is available on six platforms: iOS, Android, BlackBerry, Windows Phone, Symbian and Nokia Series 40.
Now, an interview with GigaOM has revealed that the apps is delivering 1 billion messages a day, and is used in 250 countries on 750 networks.
The firm's CEO Jan Koum told GigaOm that the secret of WhatsApp is technical stability. He said: "People appreciate a good product, a stable system. They want to communicate easily and use a product that just works."