Microsoft is testing its own smartphone design, preparing for the possibility of developing its own device, but the company hasn’t decided whether to take the device into mass production, according to the Wall Street Journal, citing unnamed officials at some of the company’s parts suppliers.

It’s the latest in a series of rumors and reports pointing to the possibility of Microsoft making a phone — presumably its own Windows Phone device — following up on the release of the company’s Surface tablet last week. The company is increasingly expanding beyond its traditional practice of solely supplying software and operating systems for devices and computers, and moving into the realm of hardware development.

As with the Surface tablet, the release of a Windows Phone device from Microsoft could pose a competitive threat to the company’s hardware partners. However, the relatively small market share of Windows Phone could make those partners more open to this type of move from Microsoft, as a way of sparking the market for Windows Phone overall.

Asked about the possibility of a Microsoft-developed phone recently, Nokia CEO Stephen Elop said, “It’s certainly a stimulant to the ecosystem. As I said earlier, we’re encouraging of HTC and Samsung and Microsoft or whomever to have devices in the market and to be making whatever investments that help spur the ecosystem on.”

Microsoft CEO Steve Ballmer has declined to comment on the possibility in recent interviews. Introducing Surface earlier this year, he said it would be part of “a whole new family of computing devices” from Microsoft, stirring speculation about a Surface phone.

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