[JURIST] A federal court in Maryland has ruled that US law enforcement agents must obtain a warrant before obtaining information from a cell phone service on the location of a cell phone user. In an opinion [PDF text] written by Judge James J. Bredar and issued Monday, the court noted that although the Fourth Amendment [text] does not protect cell phone users who use their phones in public, probable cause is still required because the individual targeted by the search may use the phone from their home, which has clearly established Fourth Amendment protections. According to court documents, in addition to being able to monitor cell phone calls, under federal regulations cell phone providers must be able to locate 67 percent of cell phone users to within 300 feet, and 95 percent of users to within 900 feet by the end of the year. Bloomberg has more.