It's not an iPhone. I noticed 3 differences. One, there is no speaker for the ear. Two, the sleep-wake button is on the left side of the device (on the iPhone, it's on the right side when looking at the front). Three, the buttons are black as opposed to silver colored buttons on the iPhone 3G.
Edit: Also, the corners are slightly pointier on the iPod touch than they are on the iPhone 3G.