(Telecompaper) Mobile messaging service WhatsApp plans to add voice calls in the second quarter of this year, its chief executive Jan Koum said in a speech at Mobile World Congress in Barcelona. The WhatsApp voice service will first begin with Android and iPhone apps, Koum said, and will expand later to Windows Phone and some BlackBerry phones, Cnet reports. Koum said WhatsApp's acquisition by Facebook would not alter his roadmap to develop the product to reach the next 1 billion users. No advertising will added to the service, he said. Facebook CEO Mark Zuckerberg was scheduled speak later the same day at MWC. WhatsApp's Koum also sought to cast himself as a partner to telecom operators and not simply a competitor, Reuters reports from Barcelona. He announced a partnership with E-Plus, the KPN operator soon to be sold to Telefonica, under which the companies will launch a WhatsApp-branded mobile service in Germany.