Usually it's MPEG4.
Mobile phones use 3GP, a simplified version of MPEG-4 Part 12 (a.k.a MPEG-4/JPEG2000 ISO Base Media file format), with the .3gp and .3g2 extensions. These files also store non-MPEG-4 data (H.263, AMR, TX3G).
http://en.wikipedia.org/wiki/Mp4 http://www.3gpp.org/ftp/tsg_sa/TSG_S.../SP-040643.pdf
Nokia E65 specifications :
Multimedia
Video and audio streaming (3GPP & Real Media)
Music player (MP3/AAC) and media player
Open Mobile Alliance (OMA) digital rights management (DRM) 1.0 with forward lock
http://europe.nokia.com/A4344228
LE: can you send a link to such a file for testing purposes ?