There's no public chat. You can only talk to friends and rivals. However, you can add rivals without friend codes in the game lobby, so you could just add everyone in the game if you want and then just delete them later.
Well wait... there could be something like it. Because in the first conduit, the host could choose to start the match whenever he/she wanted, so if the headbanger headset works while in a hosted lobby, then that can serve as one.