Rumours are rife that WhatsApp could be offering free VoIP (Voice Over Internet Protocol) calls to 600 million users, a report said, while casting doubts whether the service will be allowed in the UAE.

"The leaked images of the upcoming user interface show that the app has been enabled with other language translations which will be displayed at the time a person receives a call via WhatsApp," the report in Emirates 24/7 quoted the popular gaming site The Fuse Joplin as saying.

The service, if introduced, will pose a new challenge to Skype and Viber, as well as to telecom network operators worldwide.

But the service could be held back in the UAE, where VoIP services are allowed to only licensed players, the report said.

"As to what the licensees have done in unblocking Skype's website www.skype.com in the UAE, this action does not change the position of the TRA or amend the policy as this service is considered a Regulated Activity, therefore, it must be provided by a licensee,” TRA was quoted in the report.

“Should the service be provided through a partnership with a third party, both Licensees must seek approval to provide such service after fulfilling the regulatory and technical requirements of the TRA, which has not happened in the case of Skype. VoIP services through Skype are still unauthorised.”

WhatsApp which had about 450 million users at the time of Facebook's takeover in February has now swelled to over 600 million users, with a stated target of connecting "4 to 5 billion people over the next five years", according to the report.

WhatsApp has been adding about 25 million active users a month since the Facebook acquisition in February, and it seems likely that the service is now ready to roll out VoIP service before the end of this month, the report said.