BlackBLE

Finally you will be able to send information through Bluetooth to your Arduino using your iPhone!
With this app, you can connect to a Bluetooth Low Energy module HC-08 and send characters to it. With these characters you can program actions in your microcontroller to be executed when receiving. On a very simple way, press the black Bluetooth icon on the upper right screen to see the list of every HC-08 available nearby. Press the name of your module and the app will automatically connect to it. When pressing each button of the app, the character present on button label will be send through Bluetooth and you can read it in a serial protocol on the module.
Do you want more? What about rotating your iPhone and make it a joystick to control robots or whatever kind of system you want? If you rotate your device, screen will automatically changes to a joystick, with the same concept than the previous screen.
And, of course, you can receive information from bluetooth and read on your screen (maximum of 20 bytes, or 20 chars).
Now you can control whatever device using Bluetooth with your iPhone!