It seems like this is not enough:

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.