Connect an iPhone to Arduino over Bluetooth

Question

I would love to be able to let my iPhone-App communicate to my Arduino over Bluetooth. I found some Bluetooth shields that support the following protocols: BCSP, DUN, LAN, GAP S

Answer 1

Information about connecting to Bluetooth 3.0 or lower devices from stock OS iOS devices is only available after being accepted into Apple's MFi program.

Bluetooth 4.0 (BLE) is accessible both in development and commercially to iOS developers (without needing access to the MFi program), using the public Core Bluetooth framework available in iOS 5 or later on iPhone 4S, iPad 3 and later devices carrying BT4.0 on-board.

Added a few years later: There are now several BLE shields and Arduino compatible or Arduino-like products with built-in BLE (LightBlue Bean, RFduino, etc.) available in the market.