I've been using Viber without a problem with my girlfriend (AT&T iPhone 4) and my dad (Sprint Galaxy Nexus). However, I've been having a lot of trouble with getting it hooked up with my friend (Virgin Mobile HTC EVO V 4G). I see the chat mesages, but he doesnt show up under Viber contacts and if I try to call him it says that he no longer has the app installed. I've verified he does and chat works fine, so how do I get this fixed?