WHATSAPP TO START OFFERING ITS USERS VOICE CALLS BY APRIL. READ MORE HERE!!

WhatsApp Inc., the mobile messaging service that agreed to be acquired last week by Facebook Inc. FB +0.01% for $19 billion, said Monday that it would offer voice calling as early as April, allowing free phone calls among WhatsApp's 465 million users.


Jan Koum, the co-founder and chief executive of WhatsApp, also said during a speech at Mobile World Congress in Barcelona that he is hoping to expand the service to one or two billion users.

Mr. Koum said that the WhatsApp voice product would "focus on simplicity" as it has with its text-based messaging service.

He said that WhatsApp would first release a version of the voice service for Apple Inc. AAPL +0.44% 's iPhone and Google Inc. GOOG +0.72% 's Android platforms, followed by services for Microsoft Corp.'s MSFT -0.76% Windows Phone, as well as some phones by BlackBerry Ltd. BB.T +6.88% and Nokia Corp. NOK1V.HE +2.13%

"We want to continue to have that minimalistic approach to the product," he said. "We at WhatsApp want to get out of the way and let people communicate."

Mr. Koum said the voice product would "use the least amount of bandwidth, and we optimize the hell out of it."

With its move into voice calls, WhatsApp will now compete more directly with Microsoft's Skype service, which began as a platform for computers but also offers messaging and voice calls over mobile phones.

Speaking about the Facebook acquisition announcement last week, Mr. Koum said that the product wouldn't change, stressing that WhatsApp would remain independent. He alluded to Instagram, the photo-sharing service that was acquired by Facebook in 2012.

Mr. Koum said that WhatsApp was likely valuable to Facebook because "we both want to make the world more connected," though Mr. Koum stressed that WhatsApp wanted to know "as little as possible" about its users, including details such as a user's name.

"There are no plans to change anything that we do with the product today," he said, using words like "minimalistic," "utilitarian" and "uncluttered" to describe his philosophy.