What is the focal length of the iPhone camera?

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.