Other than the camera function, the major difference between the iPod touch and the iPhone is (Duh!) the phone function.
Now the gap between the two is being narrowed. The iPod touch CAN be modified to make phone calls with VOIP. See this http://gizmodo.com/339042/first-ipod-touch-voip-call
It's not clear whether the iPod touch can receive calls; I suspect it can't.
Don't expect Apple to add VOIP function to the touch since that would be a direct competition to the iPhone.
Now the gap between the two is being narrowed. The iPod touch CAN be modified to make phone calls with VOIP. See this http://gizmodo.com/339042/first-ipod-touch-voip-call
It's not clear whether the iPod touch can receive calls; I suspect it can't.
Don't expect Apple to add VOIP function to the touch since that would be a direct competition to the iPhone.