You can just turn off the breaker for the modem, why don't people just do that? Yes, you can remove the thing, but you can experiment today by doing that first step. There are tesla hackers, like this person https://twitter.com/greentheonly. They decompile the os releases and looks for new but disabled features.
Telematics units could be separate from IVI, could be hanging off elsewhere or could be independently procured and added at multiple different floors within a car company.
I envision a fun game for modern, tech-inclined car owners:
1. Turn the car on;
2. Scan the RF spectrum with SDR hooked up to a directional antenna, until you see something resembling digital TX in the waterfall graph. Note the frequency.
3. Dial in your microwave gun to that frequency, bathe the car in sweet sweet RF watts.
4. Confirm with SDR the signal is no longer there.
5. Repeat until you're reasonably confident you fried every transceiver that shouldn't be there.
(6. If the car doesn't start anymore, ask manufacturer for refund and suggest putting current protection circuits behind their radios.)
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More seriously though, step 2 might be useful to locate more antennas to snip. Like a fox hunt, but in your garage.