Why don't you go for a MiFi look alike approach? http://shop.ee.co.uk/dongles/pay-monthly-mobile-broadband/gallery?search=%3Abest-sellers%3ASpeed%3ADouble%20speed%204G&bundleNo=-1
At least it's more cost efficient and it will allow you to follow the latest wireless technologies. Soon all carriers will upgrade their LTE network to LTE advanced bundling different frequency bands enabling higher throughputs and better coverage. Car manufacturers are by default always slow in adapting new consumer technologies, so quite soon you will be stuck with an outdated LTE hotspot/stick.