Unlock The Noise Tanks
Get a Jet ranking on all Benten-Cho levels.

Unlock The Love Shockers
Get a Jet ranking on all Shibuya-Cho levels.

Unlock Professor K As Playable Character
Play through the game (beat ''Final Stage'') and save. Professor K can now be chosen as a playable character. He is located between Garam and Beat on the character selection screen although his image is static.

Unlock Poison Jam
Beat all Kogane-Cho levels with a Jet ranking.

Change Sega Intro
Start the GBA with Jet Grind Radio and continuously press the A button until the Sega logo appears. You will hear a person scream the word Sega instead of the normal longer chorus.