I bought a used car in which the original cell subscription ran out. The only way to continue service was through the car company (which provides the service through T-Mobile) for, I think it was $30 per month or a lump sum of $450 for 3 years. It takes a T-Mobile sim card.
I tried getting the $10 per month T-Mobile sim card, but it didn't function in the car.
Since I am not up for paying that kind of money for the services, I didn't subscribe. If I ordered the service it provides:
Google maps in the navigation interface (though without the cell connection, the navigation interface is fine--it even shows speed limits)
Makes a mobile hotspot available in the car (which I can do from my phone for free)
Probably the only useful thing is: the car would be connected to the internet even when I am not in there. So, I could control some things about my car from my phone and also send a Google Maps route to the car from my home computer or my phone.
It seems to me that some of the features could be made available by better utilizing the bluetooth connection with my phone, but then I wouldn't have as much incentive to pay $30/mo. Which is a rip-off in my mind, since the data connection they want me to buy costs $10 directly from T-Mobile. Anyway, so far so good without paying the subscription. I don't feel like I'm missing out on much.