the Viber team is late on their schedule. They are currently working on the alpha version for the Z10, then they will release a beta version. Once the beta version is tested, they will release it for the Z10.
I do not know what tango is, so I guess it is not an important app.
About Skype, it is already available for the BlackBerry Z10, provided you have the OS version 10.1. Check with Avea so discover when they will release BlackBerry 10 for their subscribers.
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