Alright, a recent announcement has made things a bit more complicated on the Japanese release of this game.
Both PS3 and 360 release has their own exclusive seiyuu for the role of Juliet from the start.
PS3 version will feature
Yoko Hikasa as Juliet
360 version will have
Eri Kitamura in the same role.
That is the reason why the you keep hearing two voices for Juliet throughout the latest Japanese Trailer.
But fear not, it is said that after fulfilment of certain condition where a code is made avaliable for entry, both consoles will have access to both voice-over.
Source
Another reason to get the Japanese release, I guess. I don't think the western side of things will have enough resources to pull such a stunt.
Oh, and the western release is dated for June, according to this
article. No mention of any option for choice of langugage for voice though.