Cheat Codes
From the main menu, select Extras -> Bonus Content and enter the following codes:

sp-street - Unlock the urban combat singleplayer level
sp-village - Unlock the village singleplayer level

Cheat Codes #2
Go to the location/path where your Profile and the Saved Checkpoints are stored which is:

C:\\Documents and Settings\\[USERNAME]\\My Documents\\My Games\\Frontlines - Fuel of War

Now Look for the \'Config\' folder inside the \'GCGame\' folder. Go to the \'Config\' folder 
and look for the following .ini file : \'GCInput\'.

Open the \'GCInput\' file with notepad and search for the following lines:

[Engine.Console]
ConsoleKey=
TypeKey=
MaxScrollbackSize=1024
HistoryBot=-1

and change it to:

[Engine.Console]
ConsoleKey=tilde
TypeKey=
MaxScrollbackSize=1024
HistoryBot=-1

Now press [~] (tilde) while playing to bring up the console. Type any of the following cheat codes:

god - God Mode
loaded - All Weapons/Ammo
allammo - Max Ammo
ghost - No Clipping
playersonly - Disable AI
slomo # - Slomo Mode
walk - Walk Mode
fly - Fly Mode
allweapons - All Weapons
behindview 1 - 3rd Person View
suicide - Kill Player