All Working Grand Theft Auto Cheats - GBA

Cheat Mode
During game play press [A]+[B]+[Start] to view your cordinates and activate the cheat mode. Then use the following cheats:

[Left], [Right], [Up], [Down], [A], [A] - All Weapons
[Left], [Right], [Up], [Down], [A], [L] - 100 Armor
[Left], [Right], [Up], [Down], [L], [L] - 15,000 Dollars
[Left], [Right], [Up], [Down], [B], [B] - 100 Health
[Left], [Right], [Up], [Down], [A], [R] - Decrease Wanted Level
[Left], [Right], [Up], [Down], [R], [A] - Increase Wanted Level
[Left], [Right], [Up], [Down], [B], [R] - Toggle Gang Hostility
[Left], [Right], [Up], [Down], [R], [R] - Wanted Level 6 stars or 0 stars

Set Speed
Hold [Up]+[R] while in a car to set the speed without pressing the gas.

Unlock New Cars
Borgnine Taxi: Beat 50 Taxi missions and the taxi will be in the Portland hideout.
F-1 Racer: Beat the 18 race missions and the car will appear at the last island for the final races.

Free Rocket Launcher Ammo
Once you're on the mission Pocket Rocket, do the mission until you get the Rocket Launcher. When you get it go to your hideout, save and quit. When you begin the game you'll still have the Rocket Launcher and the mission is over. Keep on doing this until you have all the ammo you need.