A fairly believable iPhone 5 leak has emerged mentioning 4G LTE radio, a similar (if not identical) screen size / form factor, and a micro dock connector.
iMore‘s Rene Ritchie has some well connected sources who are telling him that the iPhone 5,1, as it is being referred to in iOS betas, will have: "similar if not same sized screen (currently 3.5-inch but not set in stone); 4G LTE radio; new “micro dock” connector; fall/October 2012 release."
Apart from the “micro dock” connector (which isn’t all that far fetched either), all these details seem highly plausible.
There have been numerous rumors that Apple will increase the size of its iPhone to support a 4-inch display. While that may work for other smartphone vendors, Apple seems to be fine with the 3.5-inch size of the display.
However, if there will be a larger screen on the next iPhone, it will most likely be achieved by reducing the size of the bezel - not by changing the handset’s entire form factor.
The 4G LTE radio is pretty much a given. Not only has Apple already introduced one LTE-capable device this year (the third-generation iPad), the iPhone 5 would simply appear crippled in the face of other vendor’s handsets, should it not support the standard.
Finally, the launch date.
It is still being speculated that WWDC 12 may see the iPhone 5 introduced. However, it has become increasingly apparent that Apple has moved the iPhone’s refresh cycle to the fourth quarter.
Until last year, Apple launched each and every new iPhone in summer. In 2011, the iPhone 4S broke that cycle by launching in fall.
Apple’s annual developer event this year is not expected to bring back the summer-refresh cycle. Instead, the conference will most likely focus on a new preview of OS X Mountain Lion, and iOS 6.
By simple deduction, the next-generation iPhone will most likely debut in fall as well.