I use a headless xbox running xbmc4xbox to play music on my outdoor speakers. I developed a stripped-down web interface that works well on mobile phone browsers. The idea is to be able to browse your music, add it to the current playlist, and control playback and volume. That is about it.
This interface does not work with newer versions of xbmc. It supports older versions that will run on the original xbox hardware. The simplified interfaces discussed on the wiki (like ppcdefault.asp) seem to have gone missing. This interface fills the gap for me.
To install and use this interface simply extract the contents of the zip file into the main xbmc directory, then access via web browser at: http://xbox_ip/tunes.asp
Clicking the green arrow adds folders or songs to the current playlist where they can be played with the play button. Although the current playlist can be viewed and cleared, its management is a bit quirky. For example, stopping playback and clearing the playlist does not seem to remove all the items. When new songs are added and played, playback starts with a song from the old playlist before proceeding to the new songs. This is a feature of the original web interface, so it is beyond me to debug.
Enjoy.