Thread proposes outline of bringing a Tor friendly VoIP solution to Whonix. All other zRTP solutions are UDP based without exception. Tox can use TCP but performance is not as optimal as Mumble which can work in extremely high latency environments. Coop on a common framework with Tail server could open the door for easy integration of other collaborative tools in the future.
Since Mumble doesn't understand Tor DNS, this ticket depends on T772.