Design is not just what it looks like and feels like. Design is how it works.
Steve Jobs

Despite how easy it is to write the story of how this iPhone 4 antenna snafu has to do with the esthetes at Apple being obsessed with the look of the device, I suspect that the motivation for the design change is much deeper, and likely speaks to Apple's strategy for staying ahead of the rest of the smartphone players.

On the 3GS, 3G, and original iPhones, the antenna was coiled around the bottom of the back of the phone— where you now have a smooth glass surface that seems remarkably similar to the front one. In fact, outside of the hard edges, it is this symmetry that you first notice on the device after coming from the more rounded predecessors: the back feels exactly like the front, so much so that it is sometimes a pain to figure out what the front of the device is when you are fishing for it in your pocket.

Now why would a company that seldom sacrifices function for pure looks do this, both when it is less convenient for the user and when it resulted in this controversial antenna issue (especially if the rumors are true that Apple was aware of the likely problems)?

My brother was the person who suggested the right answer to me after hearing me complain about it: because Apple is getting us ready to introduce a multi-touch panel on the back of the device, likely for simple gestures at first (think Mighty/Magic mouse) to be followed by more complex interactions most of which we can't even conceive of at this point.

Think about it: every time any of the keyboards have to come up, you've automatically lost 45% of the screen (this was the last remaining benefit of hardware keyboards on mobile devices). More importantly, imagine all of the new types of on-the-go interactions that having a touch-sensitive back would enable. Try this: if you've got an iPhone 4, hold it in the death grip position and try some swipes over the back glass with your index and middle fingers. Pretty natural right?

And yes, because Apple fans so obsessively try to read the leaves of the patent database, the obligatory proof that someone in Cupertino has thought of this.

It is precisely because this is a credible hypothesis that the smartphone platforms are so exciting. We are still so early in this type of fundamental interface/interaction innovation that there is no telling where this might go. As Steve Cheney wrote, at the hardware layer, mobile innovation is just blowing away anything that came before it in personal computing.

[One final note: despite the fact that it runs totally counter to the way Apple does things, this is exactly what I would highlight in this morning's "Antenna Gate" press release: by letting folks know why they had to suffer through an untested and novel antenna design, the company would earn back a lot of the goodwill they've lost over the past few weeks]