Since Apple's smartphone competitors have generally slimmed down their high-end offerings to 7-8mm, Apple needs to make a leap forward from 4S' 9.3mm thickness. We believe Apple will aim at 8mm or below (at least 1.4mm slimmer) for iPhone 5, in a bid to ensure brisk sales through 2014, while peers will also continue to introduce increasingly slim models next year.
As such, all iPhone 4S components that account for thickness must be slimmer, specifically, touch panel, battery and casing. Moreover, a marginal amount of space is required between the three parts for the sakes of assembly tolerance and thermal expansion of components.
Kuo says that the in-cell touch panels will reduce thickness by about 0.5mm. A metal back case will reduce thickness 0.5mm further. Finally, a thinner battery will result in a total of 1.4mm shaved from the current 9.3mm thick device.