both sport a 3.999 inch screen, measured diagonally. Besides increasing the size of the display, Apple is also adding pixels to the screen as the new models have a resolution of 640 x 1136. That's an extra 176 pixels added down. The width of the screen will remain 1.9632 but will now be 3.484 inches tall and the aspect ratio will be close to 16:9.
There is also speculation that Apple will be working to maximize the extra real estate on iOS 6 by adding a fifth row of icons (not including the stationary icons, of course) and this is where the extra pixels come in to keep the screen a Retina display. Both of these models are said to have a home button and a smaller dock connector. The new dock connector is said to be a smaller version of the current 30-pin one and is said to be in between a micro USB connector and a mini one.
Considering that the last two Apple iPhone models ended up on the floor of a bar, we would imagine that the Cupertino based firm has tightened up security in terms of who can test a unit off-campus and who gets to take a prototype home.
source: 9to5Mac via Forbes