I got this:

http://www.amazon.com/ELM327-Wireless-Diagnostic-Scanner-Smartphone/dp/B00QRE0OOA

and this:

http://www.amazon.com/RioRand-OBD-II-Extension-Diagnostic-Extender/dp/B007ZN0JKG

(the cable makes it safer plugging it in)

works really great over WiFi, except I have to make the iPhone forget the network each time I want to connect Leaf Spy to the doohickey.