We've seen mobile hotspots for cars before, but I don't think I've ever heard of one that uses the ODB-II communications port on your vehicle for power, freeing up that precious cigarette lighter for things like chargers. The ZTE Mobley is just that.
Power is, of course, provided from the ODB-II port on your vehicle, and the hotspot theoretically should only function when the vehicle is on or in accessory mode. This leaves your precious cigarette lighter free for things like chargers, and also removes the associated bulk of what is likely to be an at least semi-permanent accessory for your vehicle.
The Mobley supports up to five users simultaneously and works with AT&T's LTE network here in the US (presumably it does 3G/EDGE, too), and it's $99 if you want it commitment-free. There's no charge if you sign an annual contract, but why on earth would you? Data can either come from your existing AT&T Mobile Share plan with a $10 monthly access fee, or you can purchase it standalone at $20 a month for 1GB or $30 for 3GB. Presumably, overages are rated at $15/GB on these plans, just as the Mobile Share ones.
The Mobley should begin shipping as soon as later this week. And yes, because it is an AT&T device, you can all but guarantee it's SIM-locked to the network, so you won't be easily rigging this thing up on a prepaid T-Mobile SIM or some MVNO plan.