There are three hidden characters to unlock in Swing Away Golf and normally you would have to beat the game to be able to use them. Now all you have to do is enter a single cheat code. Go to the Main Menu and press:

L2, R2, L2, R2, UP, RIGHT, DOWN, LEFT, L1, R1.

If you get the code right you'll hear a sound and when you enter any mode (Story or Normal) the extra characters Sam, Meg and Steven will be yours to select.

At the character select screen press and hold:

SELECT + L2

While you hit X to select your character. Your character will be left handed.

At the Main Menu (not the PRESS START screen)press:

L1, R1, L2, R2, L1, R1, L2, R2, L1, R1

You can get up to 6 different sound effects for your character. Keep entering the code and listen for the sound to let you know that you entered the code correctly. Once you've gotten the sound you like you can proceed to the game as normal and have fun!

Before hitting the ball, when you see the swing meter on the screen, press L2, R1, and TRIANGLE together. Now press LEFT and RIGHT to change the ball's shape.