After seeing a player from the other team a few times that ended up being a threat I tend to remember what he looked like and what class he was running. Not that he couldn’t have changed classes by the next meeting in the gameworld, but anyone with a good battle sense should be picking up on this also.
As for the VOIP it works when a server is running with it on. Another benefit would be to look into the VOIP volume cvars, so that you can hear people when they are talking to you. Reddit Brinkkit tool has the cvars built into it(very handy).