https://www.tacomaworld.com/threads/simpler-solution-for-dis...
The most reliable way to permanently silence the cellular modem is to pull the relevant fuse. In the above case, this also disables the microphone, which I think is a positive. Unplugging the DCM entirely, however, seems to disable to right speaker, which is wired through the DCM for some reason.
I'm cynical, but unnecessarily coupling the ability to send telemetry with some feature people definitely want seems like exactly the sort of thing that would be done intentionally.
This is to provide cell phone audio during calls – if you're already inside your dashboard to remove the DCM (modem), there is an easy pin-out to restore the right speaker's music audio (which varies across Toyota models, but usually is as simple as placing a jumper across two pins of the unplugged wiring harness.
(Yeah, technically horrible but I’m sure someone will find a way)
[1] https://patents.google.com/patent/US3576576A/en
[2] https://patents.google.com/patent/US3611388A/en