Viber is a cross platform mobile app that lets you make free phone calls and send text messages to anyone who also has the application installed. Viber is already popular on iOS & Android platforms and Viber few months ago announced that they are developing a Windows Phone client.
Today Viber has told us that they are still working on Viber for Windows Phone but will be released only after their Blackberry client. Yes, they are working on a Blackberry client which will be released soon! So according to my prediction, we can expect Viber for Windows Phone client within 3 months.