There's still no official Instagram Windows Phone app in sight but the good news is there's now a Windows Phone app available which is said to be somehow approved by Instagram and therefore uses the official APIs: 6tag. Previously known as 6tagram, 6tag is the yet most full featured Instagram app for Windows Phone. It features some of the original Instagram filters like XPro-II, Earlybird, Rise, Amaro, Hudson, Lo-Fi, Sutro, Toaster, Brannan, Inkwell, Walden, Hefe, Nashville, 1977, allows video recording and sharing with cut scenes (premium feature) and supports linear and radial Tilt-Shift with blur effects for extra depth of field. All this can then be shared directly to Instagram, without any workarounds. However, there's even more.
Modified photos can also be shared to Facebook, Twitter, Flickr, Tumblr and Foursquare and 6tag allows to interact with friends through giving and receiving likes and comments on Instagram. 6tag supports Windows Phone's front and back cameras. All this comes in a - as much as possible - Instagram-kind of design which makes it really hard to differentiate it from a original Instagram app for Windows Phone - if available.
The ad-supported app (ads can be removed via in-app purchase) is now available free of charge from the Microsoft Windows Phone Marketplace but unfortunately only Windows Phone 8 is supported.
Cheers ~ Arne
Instagram 6tag 6tagram Windows_Phone_8