PachimonDotCom over on YouTube has modified electronic servos with feet to work with various iPods, iPhones, and even an iPad, transforming them from boring mp3 players to cute dancing bipeds. It may not be practical, but it would make a great weekend project for anyone who loves to tinker.
Check out his YouTube channel for the whole googly-eye series.
For this project, I have developed very simple way to control two servo motors by iPod nano: using the sound from headphone jack as PWM signal that controls the servo motors! Yes, two servos are powered by miniature 3.7V 110mAh Li-Po battery and control lines are directly connected to headphone jack! Very simple!