This morning Viber, has issued a press release through which announces that it will release a new version of Viber for Windows Phone with support for voice conversations . The new release has been developed with the support and contribution of Nokia and therefore will be an exclusive for Nokia Lumia devices.
"Also Viber is releasing a completely new version for Nokia Lumia phones running the Windows Phone 7 platform. Viber now offers Nokia Windows Phone 7 users free HD-quality phone calls and group messaging Additions to free text and photo messages. This version was developed in partnership with Nokia and is currently available Exclusively on Nokia Lumia phones."