Most cell phones use the 3gp codec for their videos. The current version of ffmpeg in the repository does not suport this codec. MPlayer uses ffmpeg as does Xine, I think. So you are not going to be able to play these on a Vector box. Your the second person to have a question about cell phone videos that I have seen.
I made a suggestion in Dweeberkity's latest multimedia disk thread that he complile ffmpeg with 3gp support.Perhaps you should make a request for an ffmpeg package compiled with 3gp support in the New Package Requests section of the forum.
<EDIT> Actually the codecs to play 3gp videos are available for mplayer and xine to use. You just can't use ffmpeg to convert them to other formats. Perhaps your phone uses another codec. Google the phone to see what codec it uses.
Thanks! That does tell the story.