So, I was thinking of sending you to the videos that I did for Crictor on just this subject but a) I can't even bring myself to watch them and b) I just checked the one video that I think is decent in the series (least amount of stumbling in that damned language they speak here) but it doesn't have subtitles yet.
Anyhoo... I agree that the answer is very portable computers. The fact that devices like the iPod Touch, N810, and even the Samsung Q1 can be used as telephones when you put a program like fring or Skype onto them is a hint in that direction. The fact that devices that are being marketed as MID's by the likes of Compal, BenQ, Lenovo and others have a slot for a 3G sim card is another hint.
People don't buy the iPhone because it makes the best phone calls. They buy it because it does so many cool computer-y things. Ditto the G1.
In an interview I did with Jeff Pulver
(again, for Crictor, but this one's in English), he talked about how it's a mistake to think of voice- or tv- (or anything else) -over-IP as being a separate thing. These are all just services that go over the same infrastructure, use the same basic tools with different tweaks. In the past they may have been completely separate, but we don't live in that past any more.
He was talking about the effect of the Internet on these markets, but our phones are part of the Network, too, even if not every voice packet gets sent via IP packets. (Although, I think it would be difficult to find a call that didn't travel over IP at some point on it's journey these days.)
So, what makes the difference between one phone handset and another in the market? It's not just how pretty it is (that's so 2000). It's what the phone can do, of course!