WhatsApp have announced plans to add a free voice-calling service to its messaging app this year.

The American company, which was sold to Facebook for $19bn last week by co-owners Jan Koum and Brian Acton, confirmed the arrival of the new feature at Mobile World Congress in Barcelona.

Koum, who made the annoucement at the event, explained that the addition of voice calls to the increasingly-popular app represents the next stage in its expansion, with the changes set to take shape "in the second quarter of this year".

While there was not a definite date given, WhatsApp users on iPhone and Android handsets will be the first to receive the new update within the next few months, with Windows and Blackberry phones set to follow at a later date.

He said: “I grew up in Russia, we had a telephone line, but a load of our neighbours didn’t. It became a shared resource for the whole apartment complex. People would come and knock on the door and ask to call their family in another city.

“We want to make sure people always have the ability to stay in touch and call their friends and family, and their loved ones, and do it easily and affordably."

WhatsApp has experienced a remarkable rise in usage following Facebook's takeover last week, with another 15 million active users taking its total tally to a reported 465m, and Koum believes the same standard of messaging on the mobile app will be reflected on the voice platform.

“The same values of the leading messaging platform in the world will be the same on voice," he stated. "We’re going to focus on simplicity and we will make sure the same gold standard will be applied.”

“We use the least amount of bandwidth out there, and have optimised the hell out of it. We’ve made sure the quality is there, though, just like the messaging functions of WhatsApp.”

In an attempt to prevent a backlash from mobile phone companies, Koum also revealed they have agreed a partnership with German mobile phone brand E-Plus which will see the company provide carrier services for WhatsApp.

He added: "We’re also really excited about partnerships with carriers. This is an example of working with carriers in established markets to bring value to the end user.”