You're assuming that the traffic sent is free to be whatever. I could easily see telcos restricting this "5G for IoT" stuff to be just traffic to designated servers, with the more permissive hotspot use a separate extra service -- at which point, you're paying for it regardless of this hack.
Do we think ford even bother with SIM cards? Lots of modern 5G devices have e-sims etc, much easier for the factory floor if SIM card can be loaded via software too. None of my families cellphones have physical sims anymore either.
In this case, take the modem chip itself. Most off-the-shelf USB/Mini-PCIe/etc modem cards use the same underlying chips, so you can just move the chip over which would contain both the eSIM as well as the original IMEI.
I can't help but chuckle at the use of the word "just" here. Sure, if we are now into reverse engineering hardware module interfaces and potentially desolder jobs on a (at a minimum) ~$20k vehicle, of which many features will stop working once you remove the module as well as triggering how many warning and service lights...
