After a few months of private testing Sonos have opened up its Amazon Alexa integration as part of an open beta. With the Amazon skill you can ask Alexa to “play pink Floyd in the living room” and it will start playing, you can also ask Alexa to “turn up the volume in the living room”, pause playback or switch to the next song. I have been testing it for a few months and it works very well. So far it works with Amazon Music as the default music source. You can start playback from the Sonos app to playback from Spotify, Apple Music and Google Play Music and then control playback via Alexa.
You can try it out now if you have a Sonos system and Amazon Echo/Dot by enabling the Sonos skill in the Amazon Alexa app.