Now, the link for that app has been found. Interestingly, if you browse the Store listing on the web, the date for the last update is back in October. However, navigating to the link on your phone and it will tell you that the last update came at the end of January, including adding support for Windows Phone 8.1.
Unfortunately, nothing else can be discerned from the app as it is private (invite only). Yes, that means you cannot download it to your device.
The good news here is the app still looks to be in active development as suggested by Sonos tech support. The bad news is we have no idea when it will release. However, we cannot imagine it will be too much longer.
Currently, Sonos is encouraging Windows Phone users to utilize third-party app Phonos until their official app hits the Store.
Sonos is growing its presence significantly, especially in the US where the somewhat pricey hardware is more likely to sell. The service works through hubs, including one that can connect to your Hi-Fi stereo system, and then placing wireless speakers anywhere in your home. Users can then select services like Pandora or Spotify to stream music to specific speakers, giving a very custom music listening experience. Recently, they have begun to air commercials on TV (we just saw one last night).
You can check out the Store listing for 'Phish Alpha', which is the codename for the app. However, you will be unable to download it.
Via: Microsoft Place; Thanks, Gabriel D., for the tip!