Instagraph is an app that posts your photos to Instagram from Windows Phone. Sure, it's not the official app. But it's about as close as you're going to get for the foreseeable future.
The makers of Instagraph have figured out a way to get photos queued up to post without using Instagram's API. And it works! The only downside is that you've got to wait a bit before the image goes completely online. Right now Instagraph only can handle up to three images per phone per day, although the developer promises that it'll be able to man a heavier load soon. The app also swaps Instagram's classic filter collection for a more practical set of real editing tools from Aviary.
Instagraph lets you taste the forbidden fruit that is Instagram on Windows Phone. It only handles the operations of editing and posting; you'll have to turn to other apps in the store that allow you to browse Instagram proper. It sure beats any other Instagram option out there, though, because it's the only instagram option.
Instagraph is £1.99 on the Windows Phone store