Popular VoIP app Viber has been released for Windows Phone to celebrate the service reaching 100 million users. That’s an impressive number of people that have been attracted to the service for its combination of free voice calls and messages, and now that the app is available for all three major mobile ecosystems then it should continue to grow. With any kind of network you need a certain amount of users to make it worthwhile to use, and it now seems that Viber has more than surpassed the mark. The new Windows Phone app is exclusively for Windows Phone handsets – while the app can be installed on phones from other vendors, the app will be limited to text messaging only. For Lumia phones though, the app should be equivalent in functionality to the iOS and Android versions. Fittingly enough, Viber have also announced that they’ll be releasing a text-only version of their app for a number of dated ecosystems, including S40, Symbian and Bada. While the operating systems are a bit behind the times in the western world, they remain popular in markets like India where Nokia’s Asha series phones have done exceptionally well. While Viber haven’t yet announced anything regarding Windows Phone 8, I expect that we’ll continue to see this partnership with Nokia continue to develop, and Viber could soon become one of the foremost Nokia Lumia 920 accessories.