In my experience, this .mid renaming business is very handset-specific. This is, after all, a mislabeled file -
midi !- mp3. If you are having problems sending mp3s labeled as mids, try sending the same file labeled with a correct extension. Another thing that might work is checking what audio types your phone supports by looking at its http accept-encoding header, and sending a file in that format. There are many databases of this kind of info online, or you can use one of the many web or
wap portals that will report this information back to you after you connect.