I've been asked whether we could use VOX (voice operated exchange) on an intercom. Basically, this means that when a user speaks into their mike, the system automatically transmits, but is muted for the rest of the time.
Theoretically, this would keep noise down on a party line (muting unwanted background noise). But, practically, this doesn't work very well. Hence, I don't attempt to use such systems.
VOX is a threshold trigger, once any audio getting into a mike is loud enough, the circuit switches on. Any audio that is loud enough will do this, not just speaking into the mike. What you get is a silent line until a mike opens, then you get a burst of loud racket. This is actually more annoying than a continual signal with a similar sound level most of the time. Particularly if it cuts in and out with a popping noise.
Trying to set the right trigger threshold is difficult. Set it too low, and it doesn't transmit everything a person says into the mike, set it too high and all manner of racket gets through.
There's a couple of timing issues, too. How quickly the circuit turns on, so that you don't miss the beginning of what they say. And how long the circuit stays on, so it's not cutting in and out between words, but does mute at the end of your sentence.
If you're in a quiet environment, already, there's no point in muting the mikes.