WhatsApp to add voice calling service

WhatsApp, the popular messaging service for smartphones that's being acquired by Facebook, will soon be offering a voice service. The introduction of free calls, revealed on the opening day of the four-day World Mobile Congress in Barcelona, Spain, would match rival application Viber's similar offering.

CEO Jan Koum said the voice service will be deployed for Android and iPhones this spring, with Blackberry and Microsoft and Nokia phones coming later. WhatsApp currently has a voice function but only in note form. This new service will be live.

"We are going to introduce voice in WhatsApp in the second quarter of the year," he told the huge tech gathering. "I think we have the best voice product out there." Koum said that he didn't expect that WhatsApp's staff would grow in number very much, saying that "we want to operate as a startup."

Relatively unknown until now in the U.S., WhatsApp is popular in other countries, both in Europe and in emerging economies. The Mountain View, California, startup already has almost twice as many users as the better known short messaging service, Twitter.

WhatsApp, which has 465 million monthly active users and 330 million daily users, will go head-to-head against other cross-platform apps by offering voice calling like BBM, Skype and Viber.