Viber have now released a version of their application for Windows smartphones which is currently exclusive to Nokia's Lumia smartphones.
Viber offers a service very similar to Skype and enables Lumia owners to make free HD video calls to other Viber users.
As well as HD video calling you can also send free text and photo messages to other Viber users, while group messaging is also possible. Viber can automatically scan your phonebook and highlight which of your friends have a Viber account, while the service also doesn't even require registration !
Viber is already available on iOS , Android, and Blackberry devices and has over 100 million users across the world so you might be surprised how many of your friends already use the service.
Nokia Lumia owners can download Viber from the Windows Phone Marketplace by clicking here. We're not sure how long Viber will be exclusive to Nokia Lumia smartphones, but we'd expect it to become available on all Windows smartphones in the next couple of months.