There are some cheats that you can unlock in God of War: Ascension on the PS3, but you don't use them like you do in other games.
The cheats in this game are tied to the collectible artifacts that are hidden throughout the game. Find an artifact, and you'll unlock the specific cheat tied to that artifact.
You won't be able to use any of these cheats until you beat the game at least once.
If you didn't get a chance to pre-order God of War: Ascension, check out the God of War: Ascension DLC on Ebay, which is probably the only way you'll be able to get them.