When its calling feature hit Android gadgets a couple weeks ago, WhatsApp founder Brian Acton said the tool would make its way to iOS soon enough. Well, today's the day. WhatsApp calling is rolling out to folks wielding Apple devices, allowing you to chat with friends and family around the world. If you'll recall, the feature uses WiFi rather than a data connection, so you won't have to worry about international rate hikes. While the new version of the app is already available at iTunes, the release notes warn that the calling feature is rolling out slowly, so it may not be available for you immediately.