Even if you set disabledVoN = 1 in server.cfg, players will still be able to use VoN in the lobby, and channelEnabled VoN will always return true, so it will appear that players are able to use VoN.
Also, if you use enableChannel to set VoN to true when disabledVoN=1, players will be able to use VoN again, but in that case the name of the player currently transmitting will not be displayed.