Could've sworn Baby D's "Let me be your fantasy" on my original SPV as a ringtone was an MP3... Maybe not?
No idea, my Qtek8080 came as a "barebone" (no contract, no SIMlock).
I also wanted to upload an MP3 ringtone. It was there and the ringtone menue showed it up. But it did not play :-(
So I checked in the registry to find that MID, MP4 (and maybe WAV and AMR, can't remember at the moment) are supported. No trace of MP3.
That's why I converted the clip into MP4 and then it played.
Maybe MP3s are playing and there are special formats, which have problems to be played on the phone, no idea.
Did you check what the manual says about it ?
(Confess, that I didn't check either :-/)