OK, got my Mobley working. According to Fast.com, 25-30 mb/sec. Some notes:
I bought it from BestBuy on eBay. I got what seems to be the usual run-around: I was able to activate it online on the AT&T site -- until I wasn't. The next day they sent me an email saying that my activation had failed and I had to go in person to an AT&T store. So I did, after a bit of confusion at the store they found the $20 plan, activated me and it was working. I started getting emails from AT&T about my account, but when I went to the AT&T website they said I had no account and there was no account listed with my email. None of the emails had my account number, but they did have a phone number they had given me. What I eventually figure out was I had to register for a new AT&T account online. Then I put in my phone number, they sent a confirmation email to my email, and I was able to get it all linked. Someone upthread called AT&T "disorganized" and that's pretty much it, I have to wonder if every new customer has to go through this, and if so, how they have any customers at all.
I did have to pay a $45 activation fee, which I wasn't supposed to, but I'm going to eat it. The local blood bank pays $50 for a plasma donation, I've never done it but I use that as my guideline when deciding whether something is worth the aggravation. I'd rather lose a pint of blood than deal with AT&T customer support any more. I guess that's part of their business model.
Right now I'm powering it off of the USB port on my computer using this 12V step-up converter:
Amazon.com: KUNCAN Dc 5v to Dc 12v Converter Step Up Voltage Converter 5ft Am to Dc 5.5 x 2.1mm: Electronics
I happened to have a Tamiya style connector in my junk box, the female pins fit nicely onto the male pins of the OBD-2 connector on the Mobley and crimp onto the wire. Positive to pin 16 and negative to pin 4. Here's a similar connector on Amazon:
Amazon.com: Duratrax Battery Connectors Unwired (2-Piece): Toys & Games
Once I've used it enough to develop confidence I will try connecting it to my router using the USB port on the side and seeing if it can power the whole household.
I fully expect that somewhere in a conference room an AT&T executive is saying, "We're doing what?!" and this plan will come to a crashing end. But I'll enjoy it while I can.