A MIDI ringtone is one which has been made by synthesising individual instruments via technology. They are used in preference to polyphonic ringtones.
...midi files.
The Katana II supports MIDI and QCP ringtones.
For older cell phones, they are MIDI files with a .mid extension. Newer cell phones probably accept .mp3, .mp4, .aac, and .wav. And maybe other proprietary formats.
It doesn't play midi files
A .midi file is a really small sound file. You can easily find these by going to your preferred search engine and searching for ".midi songs".
MIDI files only have the notes of the performance. It is up to the sound card or program to make the actual sound. For example, to play one note of a piano sound for one second in mono at CD quality, a WAV audio file needs 44100 bytes of information. A MIDI file can do it in 14 bytes.
The file extension for MIDI Files is: .MIDA MIDI File is a 'data file'. That is, there are no sounds or audio contained in the MIDI File , just a digital set of instructions. The MIDI File data is sent to a receiving sound source like a MIDI File Player (such as the MERISH PLUS, X-Light) or through software based MIDI sequencing programs like Sonar and Cubase (for PC) and Logic, GarageBand and Pro Tools for Mac.
The Rosegarden software for Linux is used for converting sound files into music files. It likes to use sound drivers for the MIDI. It is one of the most popular products on the market.
A sound card can have both MIDI inputs and outputs. The outputs are used to control an external device, to provide a wider range of sound than is possible with the built-in wave table.
You can convert MIDI files to scores using music notation software like Finale or Sibelius. These programs can import MIDI files and display them as sheet music that you can edit and print.
Many MIDI files on the internet are free and legal to download. Theoretically, a MIDI version of a popular song could be called a "derivative work" and be considered a form of copyright infringement, but I doubt that anyone cares that much about MIDI files anymore.