How does in-game voice chat work?

Wondering how the in-game voice chat system works? I understand there is a proximity system in place where other players around you can hear what you are saying which I think is amazing because it'll make for interesting pvp dynamics. How is the setup for mic usage though? Is the mic always open or is it a push-to-talk function? I've noticed some crews are linking their discord, I hope they don't plan on just using their own personal discords and disregarding the in-game voice system as I think that would kill some of the fun. That's just a personal opinion however. I think using discord would create a disadvantage to players who are being attacked because those users on discord can speak without others hearing them. It add a level of difficulty to orchestrate an attack but having to be quite so the enemy doesn't hear you speaking.