If you're knocked prone and then use a teleport power, such as the Eladrin Fey Step or the Assassin various shadow walking abilities, are you still prone or can you choose to 'teleport' into an upright position? Is there anything official written on this?
Catstep Boots or a Safewing Amulet let you always land on your feet after a fall, so you could teleport 5 feet up and land on your feet.
Acrobatics only makes it so you do not fall prone. That does not help if you are already prone. It would have to say that you land on your feet like the items do.
Teleporting will not remove the Prone condition.
And yes there is something official on this ..... Dungeons & Dragons Roleplaying Game Official Home Page - Article (09/19/2008)
Not necessarily.
A Teleport followed by an Acrobatic Stunt could be used if the DM permitted it. This type of thing, in fact, seems like the very purpose of Acrobatic Stunt.