At the title screen, press Left, Right, L1, R1, Circle, Square, R2, L2. If you entered the code correctly, you will hear a sound. All weapons in free patrol mode and all bonus item menu options will be unlocked.
All Missions:
At the main menu, press Down, Up, Left, Right, X, Triangle, Circle, Square
All Starting Locations (Patrol Mode):
At the main menu, press Down, Up, L2, L1, Cross, Triangle, R2, R1