More sites:
https://courses.cit.cornell.edu/ee476/FinalProjects/s2007/awr8_asl45/awr8_asl45/index.html
http://scuola.arduino.cc/en/content/arduino-comunication-iphone-using-podbreakout-v15
You chose the wrong brand of device for hacking.
Agreed. Although the camera connection kit USB port also supports MIDI over USB, so it may also be possible to get serial over USB from it, I haven't updated my iOS SDK in ages.
The newer iDevices, that have Bluetooth V4, support serial communication over BLE (Bluetooth Low Energy). There are a couple of BLE shields now available. You will need to write your own app though.
http://www.seeedstudio.com/depot/bluetooth-low-energy-shield-p-1255.html?cPath=132_134
Texas Instruments has published some demo code - http://processors.wiki.ti.com/index.php/Category:IPhone4SBLEDemo