After working closely with Nokia and HTC on the devices that would run Windows Phone 8, reports say Microsoft is looking to build a smartphone of its own.

Sources at some Microsoft's Asian suppliers spoke to the Wall Street Journal about the Redmond, WA company testing a smartphone design with a four to five-inch display. It's not yet known what Microsoft intends to do with the device.

With the release of the Surface tablet, a Microsoft-branded smartphone wouldn't be much of a surprise. However, we're not sure how happy Nokia and HTC would be about its new competition.

Microsoft CEO Steve Ballmer declined to comment on whether the company was building its own phone, saying "We're quite happy this holiday [season] going to market hard with Nokia, Samsung and HTC."

Related: HTC 8X Review

[WSJ via Business Insider]