I am working on camera pose estimation. For this, I need the focal length of my smartphone camera in pixels. (My phone is HTC Wildfire S, with Android 2.3).
This is really easy. Matlab camera calibration toolbox (Bouquet) or OpenCV camera calibration will do this for you if you take 10-20 images of a checkerboard. The intrinsic parameters give you the true center of the lens in pixels and the focal length in pixels. It will be pretty close to [focal length in mm]*[resolution]/[sensor size in mm], but due to mechanical inaccuracies not close enough for accurate pose estimation.