I rediscovered my Nokia video cable, got all excited and tried to play an avi through my mobile... d'oh! All was not lost though, it has to be mpeg4 format, woohoo! - WinFF works with Ubuntu (and Windows) and will convert video files to mobile phone and iPhone formats, simplez...
WinFF - Free Video Converter
Convert your videos quickly, easily, and all at once with WinFF and FFmpeg