Just downloaded the Media Streamer application for the Nokia 770 and as a quick test have it playing my served Audio from the Twonky and/or TVersity UPnP Media servers running on my PC. This means that any UPnP server running on a Mac, Linux, Windows PC's should work with the Media Streamer on the Nokia 770. (No need to purchase SlimCenter etc)

There are UPnP Servers for Linux such as GMediaServer

Note: I have not tried Linux Versions of UPnP Media Servers so cannot comment on best of breed etc.

The Nokia 770 Media Streamer application is a very good Find

---edit---Been streaming music using the Twonky Media Server, whilst the Media streamer can see Tversity as a UPnP Server I am having problems viewing the share ATM.

Note, I do not see functionality within the current Media streamer to advise it to play the music not on my Nokia 770 but on for example my SL300i UPnP Media player. (So where is the controller element?)

The current version can see my Pictures and Video folders etc shared by the UPnP Server, but whilst named items can be selected and added to playlist, Pictures and Videos do not invoke the required result. (Player tries to play them, does not crash or anything, just nothing happens...)

These are my early evaluation results...