Yes, when I bought my Mobley back in June, I had no other AT&T accounts, and my bill is around $22 per month with tax.
You need to talk to a connected car specialist, or have the local agent look through the plans in detail in the computer for the $20 per month connected car plan which is only available for the Mobley, it is NOT the $20 add on data plan which only shares minutes with an existing plan.