I honestly was wondering the other day if there was an odb-II app. Turns out theres an app for that. Seems to be a great product idea, about time too!
From Griffin:
Features
Wireless car computer monitor, compatible with most passenger vehicles built since 1996
Wireless On-Board Diagnostic II reader/logger interfaces with your mobile phone or smartphone via Bluetooth
Gathers OBD-II data including acceleration, top speed, fuel consumption, fault and pending codes
CleanDrive App (a free download) analyzes data and displays it instantaneously in an easy-to-read graphic format
Instantaneous trip and long-term data analysis equips drivers to drive more fuel-efficiently
Compatible with:
iPhone, iPad, iPod touch running iOS 4.0 or later
Automobiles built in 1996 and later which use an OBD-II port to interface with
their on-board computers
http://www.griffintechnology.com/products/cartrip