Yes, I tried to make the MIDI file the ringing tone for my Nokia 3200 and I did it. IAfter converting them to SP midi, I put them in my phone. But I must say that not all of them worked. When I tried to open some of them, a message appeared "Unable to open file". No idea why. They were all in the same folder.
some MIDI files can't be opened on some Nokia phones (for example 3200) because the instruments used in these files are very "heavy" for the device. you can experiment changing them to others. but it's not easy to find the right set of instruments. i have the same problem