For Android and iOS.
Nintendo announced that the brand new Nintendo Switch Online App is now available for Android and iOS devices. Right now, the app supports Splatoon 2 and you can invite your friends to online matches and use the voice chat feature. SplatNet 2 also lets you invite people to private battles, league battles, Splatfest battles and such.
Yes, it is more like a Splatoon 2 app more than Nintendo Switch app, yet it is to chance. More games will be added over time.
Until the Switch’s online service officially launches in 2018, the app will be free. After the launch, a membership will cost $20/year.
In order to use the app, your iPhone must have iOS 9.0 or later and for Android, it must be 4.4 or later. Nintendo Switch app supports English, French, Spanish, Japanese, German, Dutch, Russian, Portuguese, and Italian.
Splatoon 2 will be out on July 21 for Nintendo Switch and seems like this app will be a great support to the game.
For more detailed information and FAQ, you can visit here.