X-bit Labs writes Apple is said to be evaluating 4.8" to 6" screens for a future iPhone:
Apple has always argued that smartphones with larger displays could not be operated comfortably with one hand. Besides, big screens consume a lot of power and thus shorten battery life of a device. Nonetheless, sales of smartphones with 4.8” and even larger displays are growing, which means Apple is losing market share.
Apple’s upcoming iPhone 5S and iPhone 5C are expected to have identical 4” displays. Nonetheless, introduction of the affordable “5C” model clearly breaks Apple’s “single device” approach to iPhone that has existed for over six years now. Therefore, eventually it could adopt multi-size strategy for the smartphone family as well. At the end, the company already offers different models of iPod personal digital media players.