No, that's the best interpretation of the policy, but it's not what they're doing: apparently they're only charging $2/month if you don't call enough for AT&T's taste.
It's not a customer friendly policy, as it just serves to squeeze $2 from customers who aren't using more services. But it's not criminal to add a service fee(as much as I hate it as well).
It's a cost that can't be quantified to the customer. Why not just jack the monthly cost instead of tacking on a ghost charge?