If you're a big Splatoon 2 fan you might be interested know that it is possible to use voice chat within the game without the need to use the Nintendo Online smartphone companion app. This functionality only works in LAN mode, however, and it isn't particularly great - as you can hear if you watch IGN's test video below.
If you want to give LAN voice chat a try for yourself, simply head into Splatoon 2's Shoal lobby while holding down the left thumbstick along with L+R. You'll then be in LAN mode; plug in some headphones which also have a mic and you will be able to chat to any other players on your network.
While it's neat that you don't need to rely on the Switch mobile app for LAN play over a wide-ish local area or in a noisy tournament environment, the sound quality is pretty awful. We'll stick with the app or third-party options.