I have the grandfathered unlimited data plan with the 450 minutes talk. All told, it's $80/mo. The AT&T plan compare tool shows it would be $140/mo for the 10GB mobile share plan for the 1 device. So, this is the plan I can get for $100/mo with 20GB/mo? Is this new plan technically their Next plan? I'm not clear on how the Next/Mobile Share plan works when you buy a new iPhone (which I did on 9/12). I'd really like to have a hotspot.
Sounds like you're on contract. The 100 is basically the 20gb mobile share plan with hotspot, the 40 is your line access fee. As mentioned before, it's 15 if you BYOD or go with Next, 40 if you're in contract. Next allows you to buy your phone in full amount with 0% financing, it usually is around 27 to 35 depending on the iPhone you pick.
So if you were on next it would be 100 plus 15 plus whatever the monthly installment payment of your phone (next)