Instagram has catapulted to major success, winning iPhone’s app of the year and spawning an entire ecosystem of smartphone photo products. Despite its enormous popularity, the app has remained rather simple, with only one major upgrade being issued and the team staying relatively small.

But an Android app has always been the biggest priority for Instagram, and CEO Kevin Systrom confirmed as much during Le Web this year.

Now, it appears that Windows Phone 7 users will get their hands on the much-anticipated app first. Insiders tell FastCompany that just may be the case. “A source recently left the impression that the Windows Phone team has possibly been working with the folks from Instagram,” says the site. Systrom would not confirm or deny the rumor. “Other than having pre-announced Android, we don’t comment on roadmap stuff.”

Momentum has been building for WP7. The Nokia Lumia 900 has been incredibly well-received, and Microsoft has been hard at work fine-tuning built-in features for its fleet of phones. Of course, all along Windows Phone has been praised for its metro user interface, which Microsoft has been unifying across its products.

But the platform has struggled with apps—in comparison with Android and iOS. It would be a huge coup to get Instagram on board before its major competitor, and also act as a signal for other developers out there playing the wait-and-see game with WP7. WP7 may have pundits rooting for it, but consumers aren’t going to leave their current mobile operating system if they can’t take their apps with them. And Instagram has one of the most loyal user bases out there.

Obviously, the news has to make Android sweat a little. Systrom said that an Android app was due by the end of 2012, though, so it can’t be too far off in the future if his initial projections were correct. But it’s more what deferring to WP7 says about the market competition—that the tide might be turning for developers.