WhatsApp, the Facebook-owned messaging service with 800 million users, now supports voice calling on iOS.

Already, the service had allowed Android users to make voice calls, but until now, those on iOS had to wait.

At F8, Facebook’s developers conference last month, WhatsApp cofounder Brian Acton said that the functionality was coming in a “couple weeks,” although when asked directly by VentureBeat, he said it would be more like “several” weeks. In the end, it worked out to about four weeks.

During an F8 panel, Acton said WhatsApp had spent the past year refining and iterating voice calling before launching it on Android. To date, there had been ways to use the voice calling feature on iOS, and screenshots of the implementation had circulated, but it required a jailbroken iPhone. Now, everyone with one of Apple’s mobile devices will be able to make calls to each other via WhatsApp, although the feature will be rolled out slowly over the coming weeks.

On iTunes, WhatsApp wrote — in official app update release language — that calls made via the service “use your phone’s Internet connection rather than your cellular plan’s voice minutes.” That means users may incur data charges, but won’t have to burn their carrier minutes.