I just installed Viber today, and when I am connected to Wifi it says "Viber service is currently being blocked. Please try again later. Place a regular call instead?"
When I disconnect my wifi then it works. One of my colleagues also installed today, but her samsung works perfectly connected to the same wifi network.
I am from south africa on MTN network with a Samsung Galaxy S4. Wifi connection is a Telkom ADSL line.