Police can now serch unprotected cell phones without a warrant according to a recent appeal court ruling in Canada.
This means that if your phone is not password protected and you are stopped by police they can look at its contents. In the case of Kevin Fearon the contents of his phone (picutres of guns, cash, and texts) led to his conviction of armed robbery.
While most of us have nothing to hide from the police it is still wise to password protect your phone if you want to prevent the police from searching it without a warrant. You can read the entire decision here.