so i am wondering, did you ever think of ptt: which is press to talk system. Socom has this system and it works really really well. people in socom use the system to call out commands only and its the prefect system for voip.
other features from socom in this matter is that only one person in the team can speak at a time.
also as a extra addition a time limit while talking.
this should be an option and if you dont have any buttons to put PTT, then maybe integrating into an already existing button function such as: press the button to open the command wheel or hold it down to talk.
this should be another option instead of talking or not talking set up
you should have no talking, PTT, and party chat
were party chat is were if you have a party of friends you can talk freely with them while the other members of your team cant. because with games like cod people are using mics as a free chatting sevice with friends, and are using it as chatting and playing at the same time so its enjoyable.