Remember my article about using Jitsi?
While it's pretty sweet (I still hate them for their awful (security-wise) recommended installation process.), sometimes you might want to hide your location, maybe your server's one too, and Jitsi doesn't play well over Tor, at least in my experiments, but I'll be super-happy to be proven wrong.
The solution that we came up to was to setup a Murmur instance behind a hidden service, and to connect to it with Mumble.
The latency is pretty ok (less than 1.5 seconds in total, using Tor for both clients,
a hidden service for the server, the whole thing over 3G), the GUI is usable,
it's a Free software, its encryption
~ok-enough.
Although the traffic isn't end-to-end encrypted, since the server
is running on a trusted machine, behind a hidden-service, it wasn't a big deal anyway.
The Murmur server is trivial to install and to maintain, client and server are built
with a hardened toolchain by default in my distribution, the sound quality is really
impressive* likely thanks to speex, opus
and celt, even with a bandwith of 15kbit/s, …
And if you're a bit paranoid, feel free to borrow my apparmor profile ;)
TL;DR: Great software, you should use it if you want to have some voice-chat over Tor.
Funny note, I was horrified by this section from their wiki: "The default behaviour is sane, but you should add this extra flag to get a dangerous one, because why not md5 instead?".