iPhone to Power Arduino?

Hi,

so I have an iPhone 4 as well as the Redpark Serial Cable and an Arduino Uno with a Serial Shield. All those components work quite nicely together.
What I don't like about my setup, is, that while the iPhone has plenty of juice, I still need a separate power source for my Arduino.
Wouldn't it be nice to use the iPhone to power the Arduino?
Does anyone know if that is possible, and if so, how to get started?

Any help is greatly appreciated,

Christoph

Here is the pinout for iPhone's connector:

Pin 23 is 5V.

that 5v goes to a regulator to charge the battery(battery voltage is 3v or so) so you cant do that, it is a 5v in. maybe you could do something off the 3.3v pin though. you could only use the 5v pin when you have usb plugged into the iphone