Level select 
At the options screen, press L1, R1, L1, R1, L1, R1. Select 
the star field beyond what looks like the final level to play 
the original 1972 Pong.

Unlock first level in all zones 
At the zone selection screen, pause the game and press 
L1, R1, L1, R1, then resume the game.

Unlock second level in all zones 
At the zone selection screen, pause the game and press 
L2, R2, L2, R2, then resume the game.

Unlock third level in all zones and more 
At the zone selection screen, pause the game and hold 
L1 + R1 + L2 + R2, then resume the game. This also unlocks 
the secret power-ups and the three classic black and white 
Pong versions.