What I don't understand is what these manufacturers screwed up that necessitates a firmware update to keep LTE working. The only thing I can imagine is that somebody incorrectly configured their baseband with a voice-centric 3G/LTE setup (like an old LTE telephone without VoLTE support). In that configuration, if a 3G signal is missing, the car won't connect to LTE towers, because its primary function is to connect to 3G service for voice.
But that's a legacy configuration that shouldn't have even been used in new
phones after about 2013 or so. And Tesla should
never have used a voice-centric configuration for their cellular radio in the first place, much less
in 2015, when Tesla first switched to LTE.
So I'm really scratching my head. The 3G sunset should have been an absolute no-op for data-only devices like the Tesla. If it wasn't, it means somebody screwed something up. Badly.
I guess this could be caused by that weird behavior where AT&T apparently used to allow devices to be configured for voice-centric operation with VoLTE to connect even if they had a data-only subscription, but if so, that means that this is basically just a glorified contract dispute between AT&T and Tesla that AT&T could have fixed with a single bit flip in the configuration on those accounts just as easily.