The 4th Amendment requires probable cause that evidence of criminal activity will be discovered before evidence found from a warrantless search can be used in court. I imagine that they are searching for the times that the phone was used when the criminal traffic activity occurred in this case. It sounds like it is constitutional to me. As far as a pimp's phone goes, I would think that a pimp's phone could be searched if the police have probable cause to believe that they will uncover further evidence of the crime for which they are investigating. If there is a court case that ruled otherwise, I would love to read it. Sounds like it would have some interesting facts (relative to most constitutional law cases)!