As the Slashdot summary of this SFGate story makes clear, there are some big caveats on this ruling from the California Supreme Court. Warrantless searches of cell phones are only allowed after a defendant is arrested and taken into custody. The inclusion of cell phones is part of a larger rule allowing police to seize and search any personal effects.
The dissenting judges saw the massive amount of information potentially squirreled away in a modern cell phone as worthy of an additional barrier. This is consistent with rulings from other courts, including mostly notably the Ohio Supreme Court in a case from as recent as December of 2009.
In trying to reason through how a cell phone differs from other personal effects that would seem more reasonable for law enforcers to examine, I have to wonder what about a thumb drive? A personal media player? Laptops traditionally have posed more of a challenge, usual because of the addition of a password or even encryption. What about the pin codes and passwords offered by many smart phones? Would these raise the bar enough to make the California judges, or even the Supreme Court, see more of a bright line? I think there is more to consider here than just data capacity but am not clear in my own mind what would rise to the level of a domain outside of immediate and personal effects to something more like what the SCA and other laws cover in terms of stored data. (I realize the Stored Communications Act is a flawed analogy but the rulings protecting cell phones clearly beg some more definitional work.)
I haven’t seen much in the way of crypto for cell phones, beyond password safes. I wonder if rulings like these might encourage the development of encrypted alternatives to the built-in address book and other apps.