The native file format for iPhone ringtones is M4R. In order to use MIDI ringtones on your iPhone, you must first convert them to M4R. You can use iTunes and rename the resulting audio file to ...

Audio file formats span a spectrum from pristine but bulky (WAV, AIFF) through clever, lossless space savers (FLAC, ALAC) to pocket-sized workhorses (AAC, MP3) and specialty exotica (DSD, Dolby ...