Unlock all mechs & missions in Free Mission mode:
At the Title screen, switch the tuner to the following numbers and hold for one second each:
Position '0' is on the left end of the dial (9 o' clock position), position '4' is at the top of the dial (12 o' clock position) etc.
Beat the game on Normal difficulty. You'll find the Movie Viewer at the Configuration menu.
Voice select option:
Beat the game on Veteran difficulty. You'll find the Voice Select at the Configuration menu.
Desperado difficulty setting:
Beat the game on Veteran difficulty.
Beat the game on Desperado difficulty. Press Hatch + Start during play to lower your mech.
Get rank of Lieutenant Colonel. Then, press Ignition + Start during play.
Get to rank to Colonel.
Get ten decorations.
Thanks to Revolution readers Thomas Hagan and Dire Wolf!