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Originally discovered on iPod Touch Fans (and also on 9to5), it appears that the new 4th generation iPod Touch actually contains a motor that allows it to vibrate. The motor is shown in the FCC tear down photos of the device.
Apple notes the vibration alert in their iPod Touch Accessibility page:
If somebody wants to start a video call with you, youll receive an invitation -- along with a vibrating alert -- on your iPod touch asking you to join. Simply tap Accept, and the video call begins.
Vibration has been an iPhone-only feature since the original launch in 2007. The vibration has been used for silent alerts as well as a form of force-feedback in many iPhone games.
Top Rated Comments
You would need one as you don't want to have a headset on while using FaceTime. But it won't be at the bottom, mainly because the touch isn't to be held like a phone.
The thing where the pointer points is too small and lightweight to be a vibration motor. Plus, it's too firmly attached to vibrate altogether. You need a small motor and an off-center weight to make the thing vibrate. I can't see this there.
In fact, I can't see this anywhere in the FCC teardown. I'm not saying it is definitely not there, but I looked closely at all the pics and couldn't find it.
So we have the following differences between iPhone 4 and iPod touch 4G:
1. No 3G radio and SIM slot,
2. Worse camera (only on the back?),
3. No GPS,
4. No LED flash
5. No microphone at the bottom (no noise canceling with only one mic)
6. No glass back (stainless steel instead)
7. No earpiece
8. No electronic compass
9. Higher flash sizes available
10. Longer battery life
11. Slimmer
12. Worse (no-IPS) display? (I personally doubt that)
13. No vibration motor (would be my guess from what i've seen)
edit: Can't comment on higher RAM resources, but iPhone 4 and touch 4G have the same RAM size afaik.