I have a cheap OBD-II bluetooth adapter from Amazon (~$28 IIRC) and the paid (~$5) version of Torque on an original Droid 1 phone...
The combo works fine on my wife's '99 Toyota Avalon, my '03 Chevy Astro van, and my son's '00 Ranger XLT.
Sometimes, Torque will put a grayed-out message at the bottom of the display saying "Faulty OBD-II adapter", and the older versions of the app would sometimes randomly lose connectivity, but the latest version has not lost BT connection even once. I put all the vehicle's weight, displacement, etc. in separate profiles, snap the Droid into a windshield mount and can watch MPG and other parameters as I drive... cool. Plus, there are many, many features that racers and performance buffs could use that I have never even tried.
Over the last two years I've tried literally 100's of apps, but Torque is the most awesome app EVAR!... just amazing to me the things it can do, the interface flexibility, the technology that went into it, etc, etc.