KarrdeKNR actually was refering to copyrighted mp3's, the illegal kind that should not be discussed on the forums.
However, if you are talking about legal mp3's, either royalty free or ones you have created yourself, then I can't help you with that as most free webservers do not have enough space for a simple 3 minute song. It is all a matter of how much you want to pay to upload them.