This comes up a lot and not just for traffic stops. According to the Supreme Court in a unanimous decision has said yes a warrant is required. I am researching now for the case and opinion on it. This is one of those ones, you may want to print out an keep with you, or at least have on your phone or tablet. Now the basis for the decision is that the cell phone is nothing more than a computer now days, and has to be treated as such for law enforcement searches.
from CTI Consulting http://ift.tt/2nE8oZ7