WhatsApp CEO Jan Koum announced at the MWC that the service will soon add support for real-time voice calls from within the app.

Like BBM, WhatsApp will also add support for free voice calls over Wi-Fi in the coming months. The company's CEO Jan Koum announced the significant add on  during his speech at the Mobile World Congress in Barcelona, Monday.  This is an important addition to the service, which won fame and almost half a billion users solely through its ad-free messaging support. While other competing rivals including Viber, Tango, and Skype offered voice calls over the years, WhatsApp dedicated its resources to improving the messaging side of its service.

Facebook announced its plans of acquiring the messaging platform for $19 billion, last week. The introduction of voice calls will directly put WhatsApp and its owner in competition with KakaoTalk, Line, BBM and other messaging apps with similar offering.  The service is popular in markets like South Korea, Brazil, India, South Africa and Indonesia. Though a specific date for the voice integration is not confirmed, Koum noted that the feature will first come to Android and iOS during the second quarter of this year and then expand to some Nokia and BlackBerry handsets.

WhatsApp enjoys a massive 465-million monthly active user-base and 330 million daily users accessing the service on their phones. The fast growing messaging service got 15 million users since the news of Facebook's acquisition was announced last week.

WhatsApp's move might come as a threat to some carriers with its calling alternative, but calls through phone's data means more data consumed. Carriers are betting on large consumption of mobile data in the future, so this may benefit carriers in the long run. According to a report from TechCrunch, WhatsApp has partnered with E-Plus, the German subsidiary of Dutch group KPN, to offer special tariffs to access the app.

Sudden changes in the messaging service do not mean WhatsApp is changing the way it works, Koum said. "There are no planned changes and we will continue to do what we set out to do, even after the acquisition closes. Still no marketing."