Messaging app Viber boosted its efforts to generate revenue by introducing functionality that enables users to make low-cost calls to any mobile or landline phone number.

The introduction of Viber Out brings Viber, which has more than 200 million users, into more direct competition with Skype, which also supports voice calls to “traditional” phone numbers.

Users can purchase credit within the Android or iOS Viber app via in-app purchases. By not charging connection fees and offering lower rates per minute, Viber Out offers lower call prices than competing services, according to the company.

“Viber Out gives our millions of users a new way to use Viber and ensures that they can reach any contact at any time. We will continue to improve Viber Out, keeping our users connected at the most affordable rates possible,” said Talmon Marco, Viber CEO.

Viber’s first attempt to monetise its messaging app was the introduction of its Sticker Market, which it launched at the beginning of October.

Viber Out has been added as part of the version 4.1 update of the messaging service for Android, iPhone and desktop. Windows Phone support will be added in the future.

The new update of the app also includes new content for the Sticker Market.

Messaging apps have long been cited as eroding SMS revenue for operators, but as more of them move into voice, they could have an even greater impact.