There are a few dongles you can get that plug into the OBD II port of the vehicle. I am using an old ZTE Mobley running on AT&T service. The downside to that one is it doesn't power off when the vehicle is off.
T-mobile has one called Syncup drive or something rather. That allows for multiple devices to connect as well and has GPS tracking, and Rode side assistance.
Option B is to get a portable wifi hotspot and keep it plugged in and charged in the back of the vehicle (so the sun doesn't hit it directly). Every major carrier has one of these and the prices vary.
The benefit of the hotspot is you can connect more devices (around 10) compared to the Mobley/syncup drive which allows for 5 devices at a time.
Just a suggestion but now a days almost all cell phone and cell carriers provide mobile hotspots with your cell phone/cell service (unlimited data is quite common as well). There is very little need for most any more for separate mobile hotspot devices and wifi. You end up paying for more devices and additional lines of cell service.