ArduCom will provide you with serial data communication between iPhone and Arduino. Serial-port in Arduino is connected to iPhone via headphone jack. Arducom is designed to minimized hardware and software needs. With ArduCom you can make your own simple interface and use serial ports available in Ardunio to communicate with iPhone.
Visit our website to build your own interface and learn how to program your arduino for data communication: http://arducom.shourvarzi.com