Get Every Weapon and Mission:
At the Front End Main Menu, press L1, Black, White, R1, R1, White, Black, L1.

Invincibility:
Pause the game and press L1, L1, L1, Black, L1, R1, R1, L1, Black.

Infinite Ammo:
Pause the game and press R1, L1, Black, Black, White, R1, L1, Black, White