The iPhone 4 has a 5-megapixel camera as part of the whole wonderful package. I've been experimenting with it, so . . . here are some theories, in no particular order.
─Basic quality of the files (jpgs, of course) is actually OK. Don't know how much of that is due to the camera's internal software . . . I've noticed that there's very little barrel distortion (most likely being corrected internally.) And, of course there'll be substantial sharpening taking place. Lower light scenes do have significant noise.
─I've decided that photos taken with it should be converted to black and white. At first, this was just a wholly arbitrary decision, but I've found that, as with the Canon G-series cameras, noisy images look better in black and white.
─Zoom: this is digital zoom. Again, a software thing─the camera doesn't have optical zoom. Better not to zoom, if possible. Crop in post-production.
─Ergonomics: There are no stinkin’ ergonomics. You're holding a small rectangular slab. Recommendation: horizontal (landscape) mode is going to be much more stable than vertical (portrait) mode. Use a two-handed grip. There's no shutter button, so: while holding the camera steady reach over with your index finger (or maybe your thumb) and touch the camera icon, thus taking the picture. (You can do this with either hand.)
Photo: iPhone 4, Camera Mode─Marin County, 2011