I have these lines:
disableVoN = 0;
vonCodec = 1;
vonCodecQuality = 30;
I also tried removing all three, setting vonCodecQuality = 10, removing just the vonCodec line, and just using a blank configuration -- no configuration files at all, just running armaserver.
Other things that I tried were running the server on a physical computer (it's running on a virtual machine), and trying a different Linux distribution (Debian). Voice communication works when it's running on a Windows server running on the same host, but of course I don't want to extra overhead or to need to use a Windows license for it. :)