I have white iphone4S 64G (model : MD261ZA) bought via Apple online store in Singapore last month. The camera worked well for first few weeks, though I had issues with the "NO SIM" or "NO SERVICE" which got sorted out after iOS 5.0.1 (9A406) update .... but since last week all of a sudden I have got exactly the same camea problems as you mentioned.
The rear camera would not work at all, despite my attempts to restore using DFU mode, and setting up my iPhone as new phone. However the front camera intermittently works (e.g. only if I am lucky to be able to see the camera swap icon on the shutter and toggle it to front camera then it works, but can't have this toggle button appearing everytime).
I am running out of ideas now, and would need to contact Apple Support. Unfortunately I live in another country (not in Singapore where I purchased this from), nevertheless hope they would be able to replace it for free on my next visit to Singapore.
All in all, its terrible experience & I am really upset 😟