A couple months after WhatsApp debuted its free voice calling feature on Android, the app is finally launching it on iOS.

Don’t be surprised if you don’t yet have the option to make VoIP calls, however, as WhatsApp says it’s rolling out slowly over the next few weeks.

“WhatsApp Calling: Call your friends and family using WhatsApp for free, even if they’re in another country. WhatsApp calls use your phone’s Internet connection rather than your cellular plan’s voice minutes. Data charges may apply. Note: WhatsApp Calling is rolling out slowly over the next several weeks,” says the app in its iOS changelog.

The iOS update also brings a handful of new features, like a quick camera button and the ability to send multiple videos at once.

But the free VoIP calling is the big deal, of course. WhatsApp just surpassed 800 million monthly active users, making it the biggest messaging app in the world. WhatsApp has already cut into carriers’ SMS totals, as people are more and more turning to the messaging app as an alternative to traditional texting.

And letting users make internet-based voice calls all over the world will only cut deeper.

WhatsApp hit 600 million MAUs back in August of 2014, and then crossed the 700 million threshold in January of this year. Now it’s 800 million. Keeping this pace, WhatsApp should have over a billion MAUs by year’s end.