A simple title for a simple case with a simple resolution:
Modern cell phones are not just another technological convenience. With all they contain and all they may reveal, they hold for many Americans "the privacies of life," [...] The fact that technology now allows an individual to carry such information in his hand does not make the information any less worthy of the protection for which the Founders fought. Our answer to the question of what police must do before searching a cell phone seized incident to an arrest is accordingly simple -- get a warrant.
That's right: in terms of the Fourth Amendment, the smartphone and even the flip-phone, with all of the data they contain, are not akin to patting down a pack of cigarettes in a suspect's pocket.
Search Incident to Arrest
The Court has a line of cases that boils down to this: during an arrest, the police can search an arrestee's immediate person due to the need to protect officers from possible dangers (i.e., concealed weapons on the arrestee) or to prevent destruction of evidence.
Of course, this isn't 1973. As the Court emphasized, pretty much everyone today has a cell phone, almost all of which are smartphones. Cell phones and smartphones contain a wealth of information about us -- our rolodex, libraries, pictures and videos, GPS location history, months or years worth of correspondence, and more.
In terms of the amount of information contained in one's phone, the Court felt that it was closer to the footlocker, for which a warrant was required in Chadwick, than the typical contents of one's pockets, for which no warrant is required according to Robinson. And the "exigent circumstances" exception still exists for far-fetched scenarios like cell phone bombs.
It's also important to note that the Court drew no distinction between "dumb" flip-phones and smartphones, both of which were at issue here -- the latter, obviously, holds way more information than the former. (Oddly enough, the flip-phone was afforded greater protection by the First Circuit than the smartphone was by a California Court of Appeal.)
The importance of this decision cannot be understated in terms of the Fourth Amendment and the daily searches that occur during arrests.
But, the Court's recognition that cell phones deserve special treatment in a legal context due to the immense amount of information held within, as well as the devices' ability to connect to "the cloud" (yes, the day has arrived: the Supreme Court discussed the implications of cloud computing in an opinion) could be huge elsewhere.
Off the top of our heads: what about the Border Search Doctrine? There has been debate in lower courts over whether border agents should be able to perform warrantless searches of individuals' laptops, phones, and other electronic devices as part of the exception for searches at the border: the Sixth Circuit says yes, the Ninth says no.
The government is certainly allowed to rifle through your belongings at the border, but should that apply to cell phone and smartphones as well? After today, it's an even more compelling question.