Pong (PSX)

Unlock first level:
Pause game play at the zone selection screen. Press L1, R1, L1, R1, then resume game play.


Unlock second level:
Pause game play at the zone selection screen. Press L2, R2, L2, R2, then resume game play.


Unlock third level and more:
Pause game play at the zone selection screen. Hold L1 + R1 + L2 + R2, then resume game play.


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