We have an AT&T SIM card in our smart phone on a pay as you go plan, we use the phone as a hot spot, 6gogs/month with roll over of unused data for a month. We used an AT&T data only box for a couple of years but the phone plan has the same data amount and phone service as well. The data box had a phone number to connect to AT&T but offered no phone service
I saw a posting (not sure if it was on the ROG site or the Redwood members Facebook site) that WalMart had a special AT&T deal, a SIM with 12 gigs/month at a very good price, you may want to check it out.
2013 Redwood 36RL, 2011 F-450, Sat Internet, Sat TV