Splatoon 2 (will use) the "Online Lobby and Voice Chat" Smartphone app for Nintendo Switch.
This app, linking with the game, is the (tool) to do matching in the game, and meeting up with friends invited by SNS and (friend list?), it even does voice chat.
Voice chat is also linked to the game.
For instance, in a private match, you can chat with all rendezvousing members before splitting into teams, and then the conversation changes to only speaking to those on the same team.
Now you can't converse with someone you don't know.