In Arma 2: Operation Arrowhead, the scripting command "fadeSpeech" was used to locally set the VOIP volume.
However, on my server, I globally executed 1 fadeSpeech 0; through the in-game debug console and everyone was still able to hear me talk in-game via VOIP, as I was able to hear them say so. This could be because in Arma 2 the audio setting was called "Speech" and in Arma 3 it's called "VON" and there may be some kind of out-dated reference to "Speech" still hardcoded into the command. Or maybe it's intentionally unsupported for Arma 3, I don't know.