Research->Ringtone->Formats Of Song Ringtone & Movie Ringtone
Provides information about creation and usage of original song ringtone (voice ringtone) and movie ringtone.
Formats Of Song Ringtone & Movie Ringtone
Files of song ringtone and movie ringtone are actually the same. The one that extracts audio section from the movie ringtone is the song ringtone file.
Format Name Carrier, Series Video Audio
3GPP DoCoMo FOMA
vodafone
MPEG-4 AMR
AAC
3GPP2 au WIN MPEG-4 AMR
AAC
qcp
AMC au EZmovie MPEG-4 MP3
qcp

There are formats that has only song ringtone, without image. There seems no models of mobile phones are able to play MP3 files directly. I think this is because MP3 files do not have the copyguard system that prohibits transfers.

Format Name Carrier, Series Video Audio
AMR vodafone - AMR
AAC Song Ringtone - AAC
HE-AAC(AAC Plus) au Song Ringtone(Full Version) - HE-AAC
Formats Of Vodafone
Model Video Audio Audio Details
V801SA and later MPEG4 AMR Monaural
Bitrate 4.75, 5.15, 5.90