I really doubt that Viber application is available for your device. Viber application is supported to Windows Phone 7, Blackberry, Android and iOS running devices. As far Nokia Asha is concerned it does use any of the mentioned platform. So I don't think this application is available for you. So check out for something else. If you need to confirm you can check on OVI store by setting your device and search for the app. Click on the link.