The helicopter cheat for "Grand Theft Auto: Vice City" on PC is "americahelicopter". There is no official helicopter cheat for the Playstation 2 or Playstation Portable; however, it is possible to find a helicopter within the game on both ports without a cheat.
To find a helicopter in all ports of "Grand Theft Auto: Vice City", travel to the Vice City Police Station. Once you are there, head to the rear of the police station and go up the stairs. This will lead you to the police station's roof, which also has a helicopter pad. A helicopter should be located on the helicopter pad and unlocked for the player to use.