Jitsi also doesnt run on our phones last time I checked.
Basically we have these smart-phones, awesome hardware, good devices, but we cant use them to talk confidentially with our friends.
https://bugs.freedesktop.org/show_bug.cgi?id=16891
https://bugs.freedesktop.org/show_bug.cgi?id=29904
Libpurple doesn't seem to move either: https://developer.pidgin.im/ticket/11221
Those are major libraries which are used on the desktop and mobile, and that's probably the reason why you don't see actual clients with ZRTP support.
Maybe help project Tox? https://github.com/irungentoo/ProjectTox-Core/blob/master/do...