Hold L1 + L2 + R1 + R2 at the main menu for ten seconds; a blue dialogue box labeled "Security Clearance" will appear, allowing you to enter the following codes. Hold X button and press Left or Right on the D-Pad to scroll through letters and numbers. After you enter the code, press Square. If the code is valid, it will light up yellow. The codes for all levels and bonuses will only work if you have save data from the game on your memory card. The levels and bonuses can be accessed from the box labeled "Previously on 24" on the main menu.
66BAUER - Invulnerability
62ALMEIDA - Infinite Ammo
72DESSLER - All Levels
54PALMER - All Bonuses

When on the main menu, press and hold R1-R2-L1-L2 for a few seconds and a menu will come up saying some cheats, on each letter, hold X and click left or right to get letters, then put these in

UK Version

Unlock ALL Bonuses
PALMER054

Unlock ALL Missions
DESSLER072

Infinite Ammo:
ALMEIDA062

Invulnerable:
BAUER066

(if you are using USA version, put the numbers first)
When you have entered them, click square and the letters will turn orange, it really does work and has been tested!