Except on the East Coast where AT&T LTE is just making it to secondary cities. Audi's built-in hotspots are proprietary T-Mobile. What a waste (sorry, but their 4G doesn't cut it for 75+% of US consumers).

Being said, I really don't see the appeal to built in LTE. It's just going to become obsolete and incompatible sooner - especially in the EU where hopping country borders means mobile data is outrageously expensive. I can tether to my iPhone and iPad (granted, both Verizon) and the only possible plus I can see would be if the car's antenna works a lot better.