There's a Spotifty application in the Android marketplace, but before you get too excited - it's not an official one. It's called Droidify and has been put together by a Swedish coder who got bored of waiting for the legitimate version.
From the video above, which is unfortunately in French, it appears to sync between the desktop client and mobile client reasonably well and plays music over Wi-Fi and 3G. However, it doesn't have the killer offline playback functionality that the official app promises.
The app is free, but you'll need a premium account to use it, and be aware that it might be pulled without warning - we assume it uses the libspotify API, which was still heavily restricted last we heard. (Update: see below)
"With the level of interest surrounding Spotify's upcoming move onto
the mobile platform, we've seen a handful of efforts to bring the app
unofficially to life prior to launch. The example you've seen has been
around for some time now, and although it would require a Premium
subscription it doesn't comply with our terms and conditions. We think
it's safe to say that music fans will prefer using the official, user-
friendly version once we launch", a spokesperson for Spotify told Pocket-lint.
There's still no word on the iPhone app, and rumours that Apple has said "no" were denied by Spotify, which says it's still not heard back from Cupertino.
Update: As commenters Asator and BZ point out, the application in the Android store is not that pictured in the video above by the French coder. The French coder had difficulties getting OGG streaming to work. It's from a Swedish programmer instead.
Also, it doesn't use the libspotify API, it instead uses code derived from the despotify project, which also breaks the company's T&Cs. Either way, if you download it, don't expect it to last too long.
Update: We were right, the application's been pulled by the developer following a request from Spotify.