Viber Brings Voice Calls to Blackberry OS
Viber is a cross-platform app which is currently available in iOS, Windows phone 8, Bada, S40 and Symbian.
Although Viber works great on OS 5 and OS 7 it is not supported by Blackberry OS 6 due to inherent limitations of the operating system.
You can check it out to see more specifications and features on their website.
Download Viber v2.4 with voice calling