Popular VoIP app Viber has passed a significant milestone, attracting more than 100 million users with its combination of free voice calls and messaging — and to celebrate the occasion, the company has announced the release of a new Windows Phone 7 app exclusively for Nokia's Lumia smartphone line. While non-Nokia Windows Phones are limited to messaging, Lumia users can now take advantage of the app's full VoIP functionality, mirroring features which have been available to iOS and Android users for some time.

Deepening its partnership with the Finnish manufacturer, Viber has also announced a new, messaging-only version of the app for Nokia's aging S40 platform, as well as versions for Symbian and Bada. As the press release points out, more than 1.5 billion S40 devices have been released since the system's debut in 1999, and it remains a popular platform in markets such as India, where Nokia's Asha line sells in large quantities. It is not yet clear whether Viber has plans to develop a version of the app for Windows Phone 8, but the expected release of Nokia's new Lumia 920 and 820 devices later this year could present another opportunity for an exclusive partnership.