The lobby voice chat in FM7 never worked very well. It always discontinued function after a while, at least for a few players in the lobby.
I play with a bigger group of players bon a regular basis. We can only use party if we are under 16 drivers. We are able to use Skype, and we will try out discord. But the easiest would be if the lobby chat from the game will work. Its also better for inviting new players, or when someone joins spontaneous.
Conversation is part of the online gaming fun for myself.