iPod Touch teardowns have been problematic
All our iPhone teardowns have gone well. Most of the iPod Touch teardowns have not. The most common problem we ran into was opening the case without damaging the LCD display or cracking the front glass panel (digitizer). If you're going to open an iPod Touch, you'll need to use a heat gun or hair dryer to loose the very strong adhesive that holds the display/digitizer assembly in place. I also recommend a plastic case opening tool (available online) to avoid damaging the LCD. A lot of patience also helps.