Blackberry, manufactured by the Canadian firm Research In Motion (RIM), has become the latest smartphone to offer free wi-fi calls to users via its own software.
RIM has added the facility to its Blackberry Messenger (BBM) app, which already offered an alternative to text messages.
BBM Voice will only work if both caller and recipient are using the program, the BBC reports.
BBM has earlier been able to send voice notes, and other Blackberry apps like TringMe and MobileVoip already offer access to free calls.
However, users will now be able to use BBM's popular text tool at the same time as they are having a free phone conversation, the report said.
It marks the firm's latest effort to keep users loyal to the platform ahead of the much-delayed release of the Blackberry 10 operating system, it added. (ANI)