Blizzard have officially released the Blizzard Battle.Net mobile app. This app is perfect for... well, not much at present. Currently the app only allows users to add friends, chat and see which games your friends are currently playing.
"If you've ever wanted to see what games your friends are playing while you're headed home on the bus, or quickly add a new friend you've met out on the town, now you can with the Blizzard Battle.net mobile app. Available for iOS and Android, the Blizzard Battle.net mobile app brings social features from the Blizzard Battle.net desktop app to your phone" said Blizzard.
Currently, the Blizzard Battle.net app is separate from the Blizzard Mobile Authenticator, I would expect these app's to merge and mirror Steam's mobile app over time. The app is available now via the iTunes App Store and Google Play Store.