Aqua-Soft ForumsIts both costly and timely to implement.
Add size to that.
Then remember, what el Jobso commented on 3G for first iPhone. Why they didn't incorporate it in first iPhone. Because 1) it made iPhone fat with current available tech (3G chip, circuits) 2) It was bit of a load on battery (read: not very power efficient). The same applies to camera circuitry more or less. Then there is zoom which is absolutely pointless if it's not optical. and Optical zoom means moving lens parts, again effecting the size of device.
So, when I say that tech is not here... I mean it seriously not here. Not just some half-assed implementation done in current camera phones. Two main things needs some revolutionary downsizing to get actual good camera in cellphone, sensor and optics... and image processor that isn't pig on battery.
If you want to understand why I call sensors in cell phones half-assed then take a look at following article series on Anandtech. It primarily focus on sensors on dedicated camera, but it should give fair idea how smaller sensors effects picture quality.
http://www.anandtech.com/digitalcameras/showdoc.aspx?i=3290