Not sure if VARA modem supports connections with multiple stations simultaneously but if it does, a group chat would be a fantastic addition to PtP chats! This would mean joining all stations within coverage and who hear each other (or a master station) to chat together similar to IRC channel, for example.
If not all stations hear eac other, other stations could relay the messages onwards. Maybe this needs a solution of TDMA of some sort then?
Identification of membership to a certain group chat could be similar to a service ID used in WinLink.