The trailer below is one of those 3D ones and is very convincing. It features Matt Smith, David Tennant and John Hurt, plus I think there is a glimpse of Billie Piper.
Have a watch of it below as it is very good.
Did you enjoy that? I did.
Turns out it is apparently an extremely well made fake. The fact the video tube user is called John Smith is a nice touch.
Thanks to Liz Escadale for the link.