Need for Speed Underground Cheats for Gameboy Advance
When you have completed 'Go Underground' mode ALL the cars and Upgrades in the game will become available options.
When you first start "Go Underground" mode, select the Subaru Impreza and beat the first 10 people. When you beat them it will say some thing. Then do the drag races first until you get up to the top of the drag race list. Then do the drift races until you get up to the top of the drift race list. Then do the circuit races until you get up to the top of the circuit race list. Last do the sprint races until you get up to the top of the sprint race list. Anytime you should get challenges from other racers. Beat them and move on. When you get to the top of all the lists it should "Congratulations! You are king of the racing world." or something like that. Well guess what, you won.