On the Battlefield blog you can read about the upcoming alpha test, but don't even bother trying to get access to it unless you'd like to receive the Battlefield newsletter and, far more importantly, you've got an up-to-date Veteran status…whatever that is. Seriously, I don't play the Battlefield games, as they bore the hell out of me. I don't know what Veteran status is. Regardless, invites are being sent out at this very moment!
The beta, on the other hand, will presumably be open to everyone, but won't start until sometime in Septermber. If you decide to buy the Medal of Honor Limited Edition, you're guaranteed a key, though, which is kind of obligatory at this point.