Smoothwall running a release or update earlier than Kenilworth will find Viber is not working, or only working partially. After a few rings, viber will say it has answered, and will hang up the call.
How do I allow Viber through the Smoothwall?
Create a firewall rule(s) that allow the following ports;
See our help topic, Adding new Firewall rules, for customers running Inverness or higher.