Unlocks all levels & planes
On the main menu you must tap left and right shift buttons, you will hear someone say "ok good" and this should have unlocked everything.
[Submitted by:Robin Gilchrist]

Fly a car
Complete Sky Mission Attack 1 through 8 with the dolphin.

Bonus options
Enter TASCAS as a name. Select the "Special" choice on the options menu to access "HUD", "Cockpit", and "Player Assist" options.

Cheat mode
Hold L + R and press Start when "Press Start" appears at the opening screen. The phrase "Okay, good" will be spoken to confirm correct code entry. All missions, exhibition mode, planes, and bonuses (Dolphin and Buggy) will be unlocked.

Alternately, enter IRA as a name, and "Male" as a gender to unlock all planes, bonuses (dolphin and car), and mark training mode completed with 100/100.

Fly a dolphin
Complete Sky Mission Attack 8 to unlock a dolphin that can be flown in free-flight and sky mission attack modes.

Bonus mission
Complete Sky Mission Attack 1 through 7. Sky Mission Attack 8 will be unlocked.

Exhibition mode
Complete all twenty Blue Impulse missions. Exhibition mode includes new maneuvers which were previously unavailable.

Full pause screen
Pause game play and press X + Y.

Five or six jet formation
Complete Sky Mission Attack 1 through 8. An option to fly a five or six jet formation in free flight mode will be unlocked.