There is a technology available that allows locations to broadcast commands to celphones in the area, so that the camera is simply inoperable when the phone is within the specified zone.
This was made public around Deember or so, and the baddest news is that this technology had already been installed in millions of the phones, already in service, before the announcement came.
This is similar to the discovery last year by the EFF that color photocopiers save subtle but FBI-traceable serial number info in the dither pattern of the yellow dots. This bit of steganography had been going on for years without the public's knowledge. Law enforcement can look at a color photocopy and go directly to the manufacturer and the service records of the machine to discover information about who made that copy.
Quite a lot of this stuff goes on. If you're of a forging mind, try scanning a dollar bill in Photoshop some time -- find out what happens. Your attempt will be detected and halted (the US Treasury website can provide you with legally-safe images of currency to use instead).
Feeling safe and happy about all that pr0n you've got stashed on external drive J: now?
What's uncertain is whether these anti-phone fields will be mobile -- say, attached to Jessica Simpson's car -- or whether such un-announced fields will be generally legal -- would your rights be infringed if, while having a romantic anniversary dinner with your mistress, you were unable to make a celphone snap of her simply because Justin Timberlake was lurking in some corner of the same restaurant?