Mobile messaging service WhatsApp willadd a voice call service for its customers, just days after it was bought by Facebook for $19 billion. Chief Executive Jan Koum said his aim was for WhatsApp users to be able to make calls by the second quarter, just as they can now text messages.

"We are driven by the mission that people should be able to stay in touch anywhere and affordably," Koum said at the Mobile World Congress industry fair in Barcelona on Monday.

The new could be worrying for telecom operators globally, as WhatsApp could threaten part of their revenues.

Koum also announced a partnership with German E-Plus to launch a WhatsApp-branded mobile service in Germany.