WhatsApp leads the rest of the mobile messaging field when it comes to popularity, and now the Facebook-owned service has passed 600 million monthly active users, according to CEO and founder Jan Koum.

The app crossed the significant half a billion user milestone in April this year. Tencent’s WeChat app is closest behind with 438 million active users, most of whom are likely in China, while Tango (70 million active users) and Viber (100 million active users) are among a clutch of other apps further back.

Koum’s tweet includes a sly dig at companies like Line and Kik, which only reveal registered user numbers rather than how many of that number are actually using their service.

However, the WhatsApp business model (of charging $1 per year after a year of free use) continues to look positively dated compared to more feature-centric chat ‘platforms’. Line’s revenues are growing faster than Twitter’s and Tencent is reaping lucrative rewards from WeChat’s gaming focus — so focusing on user numbers is perhaps just another side of the story.

While Koum is against introducing advertising or games to the service, Facebook will have its work cut out if it is to see financial returns on the $19 billion investment it put in to buy WhatsApp. It seems more likely that the app will be a core service designed to get mobile internet users into the Facebook ecosystem — it is the only messaging app included in the Internet.org app, for example.

Also read: WhatsApp is leading the mobile messaging battle, but will it win the war?

Image via Gabriel Bouys / AFP / Getty Images