SONiVOX

SONiVOX LP. is a U.S.-based organization that specializes in music and audio. They have provided software-synthesis solutions to many phone manufacturers over the years.

Types of SONiVOX software synths
The code-names of these synths, if one can't be found, are denoted by what it is most commonly found on.

Phones with a SONiVOX software synthesizer
Note: Android and KaiOS devices won't be listed here because they all use the same synth, and adding each one here would clutter the list.