Yes, calls work OK but if I remember correctly the voice quality is not as good as on Harmattan. (noise cancellation probably is not so good) I have no idea what is Viber for. It might be worth it as a demonstration, but not enough for everyday use as long as you cannot update to nwest versions. If you have to ask for an easy way to do it, is not good/useful good to you. For knowledgeable people the instructions are already clear.