At the Map Screen where you select which area you wanna go to. This code ONLY works at the Map Screen. I don't know if it will work if you haven't beated the game but I have beaten it. If you wanna see this code for yourself beat all the missions on the map to have the game show you this code. Also obviously it will make this game alot easier to beat and by entering this code you can also buy all the guns from the beginning.
For example to get "Infinite Money/Respect first push Sym then push * then repeat until you see you money/Respect raise, same with "Invinciblity"
Hope this helps ^_^.
*NOTE* all phones are different when using the * an #. I have the LG enV so I have to push 'SYM" then * or #, I don't know what others have to push for that.