Telephone of Sorrow: Complete the game in Normal mode. At the pause screen enter the following code: Right, Left, Right, Left, Down, Down, Up, Up, X, Y, X, X, Y, Y.
Unlock Swordfish weapon: At the pause screen enter the following code: Up, Down, Up, Down, Left, Right, Left, Right, X, Y, X and Y.
Video Gallery: Successfully complete the game to unlock the Video Gallery.
Female Voice credits: Play through the game until getting to the large courtyard just before the first chariot sequence, during your second Dark Prince transformation. Look in the corner of the courtyard to find a hole in the ceiling which enemies appear from until you leave the area. Stab and hang from the panel near that hole to open the exit. Climb the pole nearest to the hole in the ceiling to hear a monotone female voice announce the game's voice credits.