Research In Motion (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.
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.
The Blackberry 10 system is due to launch on 30 January, with the first devices running it available the following month.
BBM has previously been able to send voice notes. And other Blackberry apps – such as 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.
While the move helps bring RIM closer in line with its rivals, it still lacks the video chat functionality and 3G-support found in Apple’s Facetime, Microsoft’s Skype and Google+ Hangouts.
Microsoft and Google’s products also benefit from working on platforms apart from their own Windows Phone and Android-based systems.
But one industry watcher said the move would still be appreciated.
“It drives value to the current generation of Blackberry devices and RIM may introduce video when it launches the next system,” Graeme Neill, deputy editor of Mobile Today magazine.
“One of the key strengths of Blackberry has been its BBM ecosystem, which is still extremely popular with kids to message each other for free.
“It’s probably something RIM should have done a while ago, but it is something users will still welcome.”
BBM Voice only currently works on Blackberry 6 and 7 devices, but RIM plans to extend this to Blackberry 5 handsets at a later point.
For the time being most of the Canadian firm’s efforts are focused on ensuring Blackberry 10’s release date does not slip again.
RIM’s chief operating officer said on Tuesday that the company still aimed to be the number one mobile computing platform, despite gains made by its rivals.
“It’s not going to be easy,” Kristian Tear said. “But everybody is super-focused and super-committed. We’re going to show the world that we are turning this around.”
His comments came as research firm Gartner suggested that the company’s share of global mobile phone sales had fallen to 2.1% in the July-to-September quarter.
Samsung was in the lead with 22.9%, Nokia second with 19.2%, and Apple third with 5.5%.