To unlock all levels in the game put in the code:
Name your character LEVELS to get all levels.
To get all the levels in GTA you have to simple go to the level you are stuck at. Then steal a car and go blow yourself up, or run of a bay, get shot, get arrested, or just fine someway to die! Then after all your 5 lives are gone you should see a screen that shows you stats and press "A" when you get to the main screen, turn off the gameboy.
Turn it back on, and the level you where stuck at should be passed, now you can play the new level. Your stats will be very bad on the previous level.
Name your character KELLY or SUMNER.
Name your character FULL to get infinite ammo.
Go to the character selection screen, highlight the name Kelly and change it to Sumner. You should unlock pictures of the design team.
The following trick will advance the game to the next episode of the current level. Die or get arrested until you have no lives remaining. When the screen displaying your stats appears, press A to restart and use the same character. The next episode in the level will be unlocked. Repeat this procedure to unlock all the levels.
Note: Once you start the next episode you must pause the game and press B button to quit in order for the level to be stored in memory.
There is a hospital in North Banana Grove in Vice City. There is a tiny flight of stairs on the North end of the hospital. Climb them. Walk over the edge of the building. Once done you can walk almost anywhere in the city, even water! Cops can't even get you. You are above the ground. You can go down almost any flight of stairs to return to normal. Very useful for avoiding the cops!