You can use your own internet connection, the car connects to WiFi. As for the API, then yes, if you want to buy a fleet of Teslas and manage them with your cu

You can use your own internet connection, the car connects to WiFi. As for the API, then yes, if you want to buy a fleet of Teslas and manage them with your custom software, you need to go through Tesla. That API is a service and not a product. The car is still a product though.