Just enable it by default and put a warning in big red letters that disabling the cellular modem will also disable the ECall system, which may mean you might not get the emergency assistance you need and therefore die.
That shouldn't have to be linked. You should be able to turn off manufacturer telemetry while keeping ecall. Ecall doesn't even talk to the manufacturer. It just calls the emergency services directly.
Of course when the modem is on you can't be sure that it's not doing that but that's what we have laws for.
