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As far as I know, the camera's always had zoom. Never had a iphone though, so I could be wrong. Isn't it using the volume buttons while in the app?

Wouldn't be surprised if apple forgot zoom. I'd almost expect it now.
 
It had it since iOS 4.1. I am not sure whether iPod touches even ship with iOS 4.0. I always used it to zoom in. However, the resolution is so low, you might as well pass. Check out the user manual for iOS 4.1. The feature is stated right there.

Oh yeah. Tap on the screen to show the zoom slider if you didn't already know that.
 
I just know when I used my iPod Touch at the first time, I find it can zoom in picture mode;)
 
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