Yamaha SMAF

Yamaha Synthetic Music mobile Application Format, abbreviated as SMAF, is a file format featured on phones and other portable devices using Yamaha's SMAF sound chips. Its file extension is .mmf.

SMAF was first introduced in 1999 alongside the MA-1 sound chip, which had four 2-op FM channels. This chip was succeeded by the MA-2 the following year, which added more FM channels and one ADPCM channel. Subsequent chips added even more FM and ADPCM channels; the MA-7, released in 2005 as the last SMAF chip, introduced digital sound processor effects such as reverb and chorus.

The format and the sound chips were successful, being featured in hundreds of phones throughout the 2000s. It was the last time FM-based sound chips were used on a large scale; prior to this, FM synths were commonly found in game consoles, PC sound cards and music keyboards.

Phones with a SMAF sound generator
This list is currently incomplete.

Sources:

MMF File format
All MMF files have a header of  in hex or "MMMD" in ASCII.

SCAS
Synchronous Contents Authoring System, or SCAS, is a specification within SMAF that allows animated sprites and text to be shown with music in SMAF ringtones. It was intended to be used as a format for "animated" ringtones (PMD files can also do this, as seen on the Sanyo Katana) as well as for MMS and email greetings.

Currently, the only phones known to have SCAS content are various Anycall phones (SGH-X808, for example). Phones that don't support SCAS will play back only the music content from MMF files with SCAS content.