Unconvinced
First, prototype or not, how does the phone pictured in the iPad leak legitimize this design? I see no similarity whatsoever between them. The unit in the iPad leak has some kind of black surround (probably just someone's 3G with a silicone sleeve) and is too blurry to distinguish any of the features shown in this batch of photos.
Second, I was one of the aluminum purists who hated the transition to curved plastic in the 3G. Contrary to the popular assumption, I have neither "grown to like it" nor "changed my mind". It still reminds me of a throwback to the hard candy, clear, blobby Apple designs of the early nineties. Not to mention the dock connector cracking issues.
If the iPad, iMac, MacBook, and MacBook pro unibody theme is indicative of a broader trend in Apple product design, I see the next generation iPhone looking essentially like a smaller iPad: Seamless aluminum, flat-back with a subtle taper at the edges. And technically, they don't need to go with aluminum to accomplish that design -the back of the iMac is plastic, but still complements the design standard. What would really put it over the edge would be some flush buttons, like the battery level check and power button on the MacBook line.
Just give me an HD screen so I can ditch all the standard definition media fro mmy iTunes collection for good, and throw in a front-facing camera.
No matter what Captain Cupertino introduces, I'll buy it, and I'll l

ve it. Cuz my 3G is starting to wheeze and cough.