I have been using the built in MP3 player to play CBR & VBR 44Khz MP3 files without any problems, however, I wanted to have more control over the playback so have purchased MP3Player from Viking Informatics:
http://www.vikinggames.hu/products_mp3player.php
Unfortunately, the MP3 files wont play back correctly with this player (the sound is distorted and music sounds like it is running at the wrong speed). I have been advised by the developer that this is because of a SendoX limitation, namely, it (the hardware ?) only supports 8Khz (rather than 16Khz or higher resolution supported by Nokia phones). Because of this, the SendoX built in player has to resample 44Khz files back down to 8Khz. As MP3Player doesnt do this, this is the reason why 44Khz files wont play back correctly.
I must admit I am surprised by this as I would have thought the decoding on the SendoX would have been done in software, not hardware & if its the latter, an 8Khz limit would seem a little restrictive. Does anyone have any more information on this ?