iPhone 2012 will be 4.5" tall by 2.4" wide and have a 3.5" display or so
Here's a table of Apple's large-ish handheld devices over the past 11 years:
|iPod touch 4||4.4||2.32||0.28|
|iPod touch 2/3||4.3||2.40||0.33|
|iPod classic (160 GB)||4.1||2.40||0.41|
|iPod 5 (60/80 GB)||4.1||2.40||0.55|
|iPod 5 (30 GB)||4.1||2.40||0.43|
|iPod 4 (40 GB)||4.1||2.40||0.69|
|iPod 4 (20 GB)||4.1||2.40||0.57|
|iPod 3 (40 GB)||4.1||2.40||0.73|
|iPod 3 (10/20 GB)||4.1||2.40||0.62|
|iPod 2 (10 GB)||4.1||2.43||0.78|
|iPod 2 (5 GB)||4.1||2.43||0.72|
All numbers are in inches. The depth or thickness is the maximum thickness as the iPhone 3G/3GS and iPod touch 2/3 had curvy backs. It's not every iPod variant, but enough to give you a sense how tall and wide they were. You'll not that every single Apple device of this class is 2.31 to 2.43 inches wide and 4.1 to 4.5 inches tall. It's basically a cardinal rule that a handheld device shall be approximately 4.4 by 2.4 inches wide. The depth or thickness obviously varied with HDD size and component/chip size/features of the day and of the of the device.
How Apple arrived at a planform size of approximately 4.4 x 2.4 inches is unknown to me, but they've basically stuck with this for every single iPod (not mini/nano/shuffle), every single iPod touch and every single iPhone for 11 years now. Past performance is not an indicator of future performance, so they may change it, but 4.4 x 2.4 appears sacrosanct. They've never even experimented with a different size in a shipped device, even though they have had ample opportunity.
If they do produce an iPhone 2012 that has, say, a 4.4" 3:2 aspect ratio screen it will be a break a line of handheld devices going back 11 years. Hard to believe that they would do that. It really would be a momentous change, almost like an all new product category.
They can increase the size of the display in a couple of ways while maintaining the iPhone-ish 4.5 x 2.4 inch planform area. They can maintain the aspect ratio and decrease the size of the "bezel". There are two parts of the bezel observable in the current iPhone: a standoff distance between the LCD and the inner edge of the bezel proper; and the distance between the inner edge of the bezel and the outer edge of the iPhone. The total distance is about 0.185" in the iPhone 4/4S and 0.225" on the iPhone 2G/3G/3GS, assuming the display is precisely 3.5" diagonal. If you decrease this total distance to about 0.05" (1.27 mm), a 4.1" 3:2 display could be fit in there and it'll still be 2.4" wide. The current sized home button (0.44") will still fit, just barely.
The negative to this is who knows if a phone with display all the way to the edges could be built with the robustness and rigidity for a droppable handheld. Another negative is that it'll unbalance the negative space or the unbalance the spatial relationship between the screen and the top and bottom. It may simply not look right.
The other way is to increase the aspect ratio. Using the same 0.185" bezel distance and 2.4" total width, a 3.8" 16:10, a 4.1" 1.78:1 (HD TV aspect ratio), or a 4.5" 2:1 sized screen could fit into a 4.5 x 2.4 inch device.
Your negatives are that the home button gets shorter and shorter, to eventually needing a virtual one; the ear speaker and FFC may not even fit anymore; you'll even reduce precious thickness for the back camera; and introduce more friction for developers and users due to the different aspect ratios. The "may not look right" with unbalance display space and negative space likely applies here as well.
So, after looking through this, I'm led to believe that if Apple builds a handheld that is say 4.8 x 2.6 inches like various Android, WP7 phones, it'll be a huge sea change in Apple's thinking about how big a handheld device should be. They've used this basic size for over a decade now. It just doesn't seem like they'd do it. And considering the stresses involved of a thin bezel, increase aspect ratio would be the better bet. But that'll mean a new way to do home functionality. And I don't think they'll do 16:10 or 16:9 as there are a gazillion devices that have that. The best bet is to use the same 3.5" display.