AT&T Unlimited LTE Hotspot $20 without AT&T phones

You are not looking hard enough. They are out there and I would suggest that you start at a Corporate AT&T store. If they don't have one they can get one no matter what the sales associate says. It's only available from AT&T despite it being at ZTE product. Do a search for ZTE Mobley and see if that helps. Don't pay more than $99 and once you get the device and you get it setup be sure to have AT&T waive the $25 activation fee.