Timothy Collins, the one who called into the Vergecast a few weeks ago and shared his very clever theory on how Apple could pull off a 4-inch iPhone, writes more about how he came about his theory:

I came up with this “theory” from thinking, using logic, and simply what I want from a new iPhone, mixed with what I thought Apple would want from a new iPhone.

I think Timothy is right in his assumption that, if Apple were to bust out a 4-inch iPhone, it very well may do so without changing the physical dimensions of the current iPhone in any direction. And wouldn’t that be something just like Apple? — introducing a new form factor without designing a new form factor. Though, as we’ve discovered from the new iPad, if Apple is going to compromise to solve an engineering enigma, they will compromise on size and/or weight first.

Timothy Collins on His 4-inch iPhone Theory