Research->Ringtone->Converting Tool
This page provides information about tool that converts SMF file into ringtone.
Converting MIDI Files Into Ringtone Files
Like professional suppliers, you make music files for mobile phones by using your personal computer. You make a MIDI file first and then convert it into ringtone format such as MFI(MLD), SMAF(MMF), and CMX(PMD) by using converting tool. (Converting would not be necessary for the recent models of mobile phone that support MIDI files.)
As for professional production company, official tool that is designated by each carrier (DoCoMo, au, Vodafone) will be used in order to convert MIDI files into ringtone files.
I think this kind of tool is not available for individuals to purchase. So, as for individual, tools that are distributed as shareware or freeware would be used for converting. Please note that even if you have a file in the same format, you will have to convert and prepare a file for each model. Also, you will have to prepare different files according to 16 voice, 32 voice or 40 voice.