A normal camera is much deeper than a cellphone. At least one I'd like to carry with me ;-)

Nokia once had a cellphone with the camera on the side, mounted in the clamshell hinge. With smaller lenses it could be a side-facing camera.

Are you talking about the Nokia N93? A friend of mine had it. It was the only cell phone I'd seen with optical zoom.

It's most probably the only one where an optical zoom would fit. A quite ingenious solution. A periscope-like mount would also be viable for cellphones - it would still be at least twice as large as a common camera, but it wouldn't be much deeper.