You can get plans for the Winegard ConnecT 2 from Verizon, AT&T and several other providers. Winegard also sells their own data plan (using the AT&T network) but it is expensive compared to other plans availablle.
AT&T used to have an Unlimited Plan for $360/year but it is no longer available. I recently switch to a Cricket Simply Data Plan (using the AT&T network). They have $20GB for $35/month or $100GB for $55/Month. AT&T has similar plans.
You can sign up online or stop by a store. They will give you a Data SIM card that you will need to install in the unit on the roof (there is a SIM card in the unit for Winegard plans so you will need to remove it). Then you can activate the plan online and switch to the 4G hotspot option when you don't have WiFi.
I have had one for a couple years and it works very well. It can provide some decent coverage when your cell phone is showing one bar because of the antenna array in the unit.