Spotify has published a YouTube video of its iPhone app, which is set to be available to premium subscribers on the App Store. Well, in theory – Spotify is still awaiting Apple’s approval of the app, which has been a matter of some speculation. BBC News says the app has been submitted to Apple for approval, and could be available within days. Meanwhile, Wired’s Eliot Van Buskirk has been using the app and is impressed – “You’d have to pry it out of my cold, dead iPhone before I’ll delete it”.The Wired article claims that Spotify HASN’T chosen to include Buy links through to Apple’s iTunes Store – something that other streaming music iPhone apps have done. Could this be a problem for approval? We’ll have to wait and see.Anyway, the video shows how the playlist-caching feature works, which is what people have been getting excited about. Have a look, and let us know what you think.