Viber Apps issue with Nokia Lumia 822

My wife and I recently switch from AT&T to Verizon Wireless and both of us got the Nokia Lumia 822. She has relatives in and Puerto Rico and have relatives in the Philippines. Recently, all my friends and relatives from the Philippines told me to download an apps which is VIBER wherein I can talk and text to them without being charge international call or pay per use text message. I already download the apps but it seems that its not working even though its showing my the apps is compatible with Windows Phone? is anybody also encounrter the same problem?

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Nokia Lumia 822