We are just few days away from the launch of Instagram Windows Phone app. It seems Instagram app got already submitted to the Windows Phone Store and there is a Windows Phone Store link as well. The Windows Phone Store link page is not live yet, I guess they are waiting for the launch date. According to the people who tried this app for past few weeks, the app works pretty well without any hiccups.
You can download Instagram for Windows Phone from Instagram.com/download/windows. Here is the direct store link to download when it becomes available.