On ATT, hot spot is not part of 4LTE, it is an option on their network. When one turns on Hotspot on the Phone, it say validating that the SIM has the authority. I would doubt that Tesla would have open-ending cost on having a hot spot capacity on each vehicle.
If I understand correctly, the UI doesn't permit video streaming in the Model S. If that is the case, then the data is somewhat limited to Browser pages and OTA software updates, etc. I yield to those with more knowledge on the UI...