WhatsApp founder Jan Koum revealed on Monday that voice calling will be added to the cross-platform messaging service during Q2 2014. While we don’t know which platform it will be landing on first, or exactly how it will be implemented, it signals the first significant evolution of WhatsApp following its $19 billion acquisition by Facebook. The feature is hardly original though. BlackBerry Messenger (BBM), Line, Skype and many other messaging apps have offered voice calls for some time, although given the size of WhatsApp – it now stands at 330 million daily and 465 million monthly active users, Koum announced today – it’s important for the service to maintain its rapid growth by offering a feature set comparative to its rivals. WhatsApp is known for its simplicity, however. The app is approachable because it replaces SMS without bolting on too many peripheral, experimental or money-making features.