A Microsoft partner accidentally leaked images of the yet-to-be unveiled Windows Phone-based Nokia Ace 900 smartphone, according to a report published by PocketNow.

The Microsoft partner reportedly leaked some details of the Nokia Ace 900 by publishing its images on Christmas cards.

In the images, the smartphone looks very similar to the Nokia Lumia 800 but the images also reveal subtle differences, such as a visible front-facing photo snapper and a photo snapper button situated a bit higher.

In addition, the smartphone can be seen with an AT&T 4G logo, which brings it in line with rumors that US carrier AT&T will launch three new 4G LTE Windows Phone-based handsets sometime early next year, around the same time the Windows Phone-based Nokia Ace 900 is expected to make debut.

Various reports suggest that the Nokia Ace 900 smartphone will be launched on AT&T's 4G LTE network, with most probably the new Tango update. According to the reports, the smartphone should make debut on 18th of March.

Microsoft is spending more than $1 billion on its partnership with Nokia to achieve a strong foothold in the field of mobile operating system.

Commenting on the Redmond-based software giant's partnership with Nokia, chief executive Ballmer said, "Nokia's involvement ... will drive volume, will create new innovation and products, and will accelerate the adoption of the Windows Phone platform."

Microsoft is trying hard to convince consumers that Windows Phone-based handsets are a feasible alternative to the currently popular iPhones and Android smartphones.