Enter all cheats at the main menu and you should hear a sound:

Press X, Black, Y, White, L, R, White(2).

Hold L + R and press White, Black, Y, X(2), Y.

Press White, Black, X, Y, White, R, L, Black.

Press L, White, Y, R, White, Black, X, Y.

Press Start + Back during game play. (This doesn't work during every part of the game)