If you're a car nut, a paranoid parent, or a small business owner looking to do a little, uh, company vehicle economy analysis, Verizon's teamed up with Delphi to create the Vehicle Diagnostic system. It's actually pretty cool!
Verizon will sell you the Delphi hardware module, which should work with a majority of ODBII-compliant vehicles 1996 and later. You hook this little guy up to your vehicle's ODBII port, and it automatically starts sending data back to your web dashboard (and/or the Android app) via its built-in data connection. If you have a Verizon Share Everything plan, it will set you back $5 a month, though the data usage it brings will likely be pretty near negligible.
So, what does it do? The ODBII diagnostics integration allows you to do things like monitor your vehicle's diagnostic codes - what exactly your vehicle monitors in this fashion varies (a lot) by make and model. It could be anything from gas mileage or tire pressure status to a check engine code to track down a problem. I doubt the meanings of codes for every supported vehicle are there, but this is definitely a legitimate convenience.
You can also see things like battery status, remaining fuel, set RPM and speed alerts (eg, if the car goes above a certain RPM or speed), and even unlock / lock / start / turn off your car remotely (again, individual vehicle support for this stuff varies widely).
In addition, the module has a built-in GPS tracker, and that location data is sent to your web dashboard, so you can see where you've been, analyze your gas usage and trip patterns, or secretly stalk your ex / child / employee in a creepily efficient fashion. While vehicle tracking and diagnostics tools like this have existed for a while (there are even Bluetooth-based ODBII readers and apps), adding in a mobile data connection and Delphi's rather polished-looking software definitely makes this the most robust consumer-oriented system I've seen.