The iPhone suffers from a terrible Bluetooth design. As such, most of the apps that I've seen are paired with a device that was built to work with the iPhone. This is the only one that I've heard of:
http://www.actron.com/product_detail.php?pid=16367

It's more common for an Apple user to go buy a cheap Android phone/tablet from from Craigslist or ebay and buy the $5 Torque app. The Apple options that work are pretty expensive.