Having launched a free voice calling service for its Android users, WhatsApp is now introducing the feature to its iOS version.

According to the iTunes page for WhatsApp Version 2.12.1, “calling is rolling out slowly over the next several weeks” rather than being available to all Apple users immediately, although the process will probably be quicker than it was with Android.

In the Android version, calls can be made to a contact while chatting with them or by going through the contacts list within the app. If the user doesn’t have a version of the app supporting the feature, the caller is notified.

The calls allow users to use the speakerphone and have mute options, as well as a call duration log.

The iOS app update will also include support to send photos and videos from other apps to WhatsApp chats, and enable users to take photos inside chats and send multiple videos in one go.

WhatsApp said earlier this week it has hit 800 million monthly active users, indicating the company is maintaining its rapid growth trajectory.

In fact, it is on track to hit one billion active users by the end of 2015 – putting it comfortably ahead of its closest rivals.

The company has also introduced a web-based version of the service, although unlike other competing products, it is paired with a smartphone app.

WhatsApp was bought by Facebook last year but, unlike Facebook’s Messenger service, WhatsApp does not have a business-consumer communication or a payments platform, which has made some wonder how the service will be monetised.

But back in October, CEO Mark Zuckerberg reiterated that there were no plans to monetise WhatsApp (or Instagram) aggressively in the next couple of years as he believes the best way to fully realise the potential of the products is to initially focus on connecting more people.