You should have Viber on your smartphone.

This is optional though. As long as your PC has an existing speaker and a microphone, you can still make calls. It will just be better and clearer with a dedicated PC headset.

Wait for your friend to pick up your call. If your friend is online, you will immediately be connected and you can start talking once he accepts the call. Calling a Viber user on Viber is always free.

Viber Out requires Viber Out Credit, which costs real money. Refer to “How to Make an International Call with Viber” to determine if Viber Out is for you.