At the mission selection screen in either single
player or cooperative campaign mode, press Up,
L1, Down, R1, Left, L1, Right, R1, Up to unlock
all missions in that mode.
Pause game and go to the options menu. Then press Up, Down, Left, Right, Left, Right, L2, R2. It doesnt matter how fast you press the buttons.
During gameplay, pause the game and go to the
options category. At the options screen press
Left, Right, Up, Down, Up, Down, R2, L2.
Click Up, Down, Left, Right, A.