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.
"We are going to introduce voice in WhatsApp in the second quarter of this year," Koum said at the Mobile World Congress in Barcelona, Spain. "I think we have the best voice product out there. We use the least amount of bandwidth."
WhatsApp currently has a voice function but only in note form. This new service will be live.
On Wednesday, Facebook acquired WhatsApp for $19 billion in a deal that is by far the biggest by the social networking company and any other done by Google, Microsoft or Apple.
The blockbuster deal made serious waves with those in the telecommunications industry who gathered this week in the Catalan city, but also sparked concern among users that Facebook would introduce advertising to WhatsApp.