There's a lot going on here, which is why I didn't post about it as soon as it became news. First, the good news. The police must now usually get a search warrant to search the phone of a person whom they arrest. There are a couple of exceptions, such as fear of evidence being remotely deleted or exigent circumstances, like if you're a suspect in a kidnapping. Most of the time those exceptions won't apply.
But that doesn't mean your data is sacrosanct. Consider what's going on in Florida, where stingray devices are being used to impersonate cell towers and are being used with impunity, usually without getting a search warrant. Police can still subpoena data from your cell provider, then again, at that point they've gone through legal channels and theoretically demonstrated probable cause. It's possible that at that point that searching your phone is irrelevant and just done for form's sake.
Still, it is a good thing. It's good to know that the Supremes recognize that cell phones, and smart phones in particular, are incredibly personal and hold a huge amount of sensitive information.http://www.npr.org/blogs/thetwo-way/2014/06/25/325497536/high-court-says-police-need-a-warrant-for-most-cellphone-searches
So what happens if you are stopped and/or arrested and police try to search your phone without a warrant? Let's face it, there's not much that you can do to stop it, the threat or use of physical force would be really stupid at that point. The two best things to do is to (A) lock your phone before your arrest if you can, and (B) loudly proclaim as often as possible, preferably in front of witnesses, "I do not consent to that search." Even if police ask you a yes/no question whether they can search your phone, reply with 'I do not consent'. They're good at asking double-negative questions, such as 'You don't mind if I search your phone, do you?' How do you answer that? Answering either yes or no can be construed as consent, as can not answering. So answer 'I do not consent to this search.' Same thing goes with your car, if police want to search your car you should not consent and force them to get a proper warrant with proof of probable cause.http://www.dailydot.com/politics/stop-police-phone-search-warrant-warrantless-illegal/
Here's some info on exceptions that can allow police to search your phone:http://fivethirtyeight.com/datalab/police-can-get-access-to-your-cellphone-data-even-after-the-supreme-court-ruling/
But if there's one thing that this case has confirmed. Something which has been demonstrated time and again, is that the Supreme Court is very weak when it comes to understanding technology. One Justice was baffled that some people might carry more than one cell phone. I did that for work when I was on-call, until I asked 'Can I just forward the on-call phone to my cell?' Apparently no one, including management had thought of that. One Justice while hearing a case about patents and Ebay, suggested that he could program something like Ebay given a weekend, because it was just pictures and prices.
The Supreme Court didn't have a photocopier for 50 years after its invention. They don't use email much, and only do audio recordings of their public deliberations. They are techno-Luddites.
Part of the problem is that they are trained to reason via analogy, and that process is breaking down big-time. From the article: "... In past arguments, computers were analogized to typewriters, phone books and calculators. Video games were compared to films, comic books and Grimm’s fairy tales. Text messages were analogized to letters to the editor. A risk-hedging method was compared to horse-training and the alphabet. EBay was likened to a Ferris wheel, and also to the process of introducing a baker to a grocer. The list goes on.