If you want to write an app on the iPhone to control the GPIO pins (or really do anything on the Pi), check out my github repo:
Nothing revolutionary, but I'm not sure that a lot of people know about the usbmuxd method for communicating with the iPhone (I know I didn't). This method also works for the BeagleBone (and really any Linux computer).
And of course I used the Adafruit Raspberry Pi distribution. I think the future I would like to expand the app a bit to include some of the nice features of the Adafruit distribution.
Also check out this blog post from Alasdair Allan: http://www.dailyack.com/2012/08/blinkin ... -from.html
Really wish I had ordered my case and breakout cable before working on this project though. Will do that once they are off backorder.