I think Saldana's delivery was fine... the problem is her voice just doesn't sound like the Uhura we're used to.
I don't know... Perhaps the context of it is off or something. I just watched it again on Youtube, and it just doesn't fit. Could be her voice. I'll reserve judgment until I've seen this delivery in the film itself.
Have you got a youtube link for the trailer with Saldana's line in?
Go to this page of trekmovie http://trekmovie.com/2009/03/05/new-star-trek-trailer-online/
It's the video where it says UK version trailer