I pre-ordered the PS3 version today at GameStop and they wouldn't give me the code. They said they got an e-mail saying to hold back beta codes regardless of what system, not just 360. Lame sauce :-/
EDIT: Just tried the C&C4 method. It worked up to the point where I hit Get Your Voucher Code on MoH site. It loaded the page where the code should have been displayed but it was blank. When I retry entering the C&C4 code it says its already been used. Anyway to look up the beta key through the EA account?