With AT&T having recently revealed in an announcement that it will commence the sales of Nokia's new Lumia 900 handset from April 8, the Finland-based smartphone-maker Nokia is set to face its first real test in the North American market.

The Lumia 900 - which Nokia first announced in January this year - is an aggressively-priced high-end LTE Windows Phone handset which has been specifically designed for the consumers in the US.

Thanks to a much wider portfolio of Windows Phone 7 models, like the Lumia 800, and pervasive marketing campaigns, Finland-based handset maker Nokia surpassed all its competitors to emerge as the top-spot Windows Phone 7 seller during the 2011 fourth quarter.

According to the latest statistics put forth by Strategy Analytics, Nokia's shipments of Windows Phones touched a whopping 900,000 units in the mentioned quarter help the company leapfrog its rivals to claim the top rank, for the first time, among the world's Microsoft smartphone producers.

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.