It seems like even in base model cars, cellular connections are included and enabled for vehicle services. We recently bought a base model car, and without any sort of subscription, the car is connected to always-on cellular as such that the car can be started from a phone app.

Another manufacturer I bought a few years ago had similar capabilities, but only included a couple years of access to it before a subscription fee was involved.

My guess is car manufacturers can get a pretty special rate for cellular plans that are almost certainly IPv6 only and have extremely low/restricted usage for car telemetry.