It was a little difficult to extract much information on the purely Japanese website, but when there's a great app, there's a way right? MP3Play by Sata is a media player for your Nintendo DS that allows you to play your favorite music from your flash cart. Expect playback time and time indication of the mp3 file, ID3 tag interpretation and Japanese file name indication correspondence (UNICODE).

Changelog:

M3 professional miniSD (the projection it is not temporary correspondence
Improving the recognition order of the device.
WORK GBAMP (CF), M3-SD, M3-miniSD, SC-miniSD and SC-CF
UNTESTED M3-CF, SC-SD, EFA2 and MK2/MK3.