What Cyclebum wrote is a good summation. As to camera phones and their capacity in mega-pixels...that is all well and good but don't forget the lens being used. Camera phones have a small lens the size of a pea compared to actual cameras that have not only much larger lenses but also greater light gathering capability and higher focal lengths. Essentially you get more parameters to play with using an actual camera.

But again, what Cyclebum wrote is a good rule of thumb.