The Viber Out service allows users to make domestic and international calls over the internet. Viber Out offers a cheaper alternative to regular phone calls and it is available for all the current versions of the Viber app: Android, iOS, Windows Phones and PC (desktop app).
To use this service you first need to buy some Viber credits, or else the following message will be displayed:
Open the Viber app, tap on More > Settings & Privacy > Viber Out:
Tap on Buy Credit and choose a plan:
Proceed with the payment and that's it:
You can dial any mobile or landline number by going to the Phone menu of the Viber app > Open Keypad.
The rates for domestic and international calls are available on Viber's website: