Technical

SpringBoard is the application that manages the home screen on iOS devices. With SpringBoard, icons on the home screen can be organized, the background wallpaper changed, and applications are launched. Some of the iPhone's settings at startup are also set by the SpringBoard.

Essentially SpringBoard is like the mobile version of a desktop. Mac OS X features the Finder while Windows computers have the Explorer. In iOS 4.3.3 firmware, SpringBoard looks for apps to display on the home screen in the /var/mobile/Applications and /Applications directories on the iPhone.

No, the iPhone only has space for one SIM card. The iPhone 4 only holds one Micro SIM card.

Creative developers have enabled dual and multiple-SIM solutions for the iPhone, however these are unofficial hacks that likely violate the Apple warranty and cellular carrier terms of service. Having more than one SIM card makes it possible to use one iPhone on multiple carriers or have two phone lines on the same mobile device.

The effective or equivalent focal length of the iPhone camera varies by model. The actual focal length on the original iPhone (2G), iPhone 3G/3GS, and iPhone 4 (rear-facing main camera) is 3.85mm.

The field of view (35mm SLR camera lens equivalent) for each model is listed here:

Original iPhone (2G): 37mm
iPhone 3G: 37mm
iPhone 3GS: 37mm
iPhone 4 (rear-facing main camera): 30mm

The iPhone 4 captures a slightly wider field of view, fitting more of the scene into one photo than its predecessors.

The Apple iPhone 4 uses a Micro-SIM card.

The Micro-SIM (Subscriber Identity Module) contains the same chips as a Mini-SIM card, with less surrounding plastic. Micro-SIM cards measure only 15 x 12 x 0.76 mm. The Apple iPad Wi-Fi + 3G was the first Apple mobile device to feature the Micro-SIM.

Previous iPhone models used larger Mini-SIM cards.