Every state is different... Illinois requires you to have a front AND rear plate...
MISSOURI HOWEVER :
No Front Plate and
WikiAnswers - Is a front license plate required for your personal ...
Looks like you NEED to have a front plate s0n. The reason they do is so when there radaring your car there basically aiming at the plate because its reflective, and flat so it bounces back at them to give them an accurate reading...