Microsoft’s (MSFT) manufacturing partners felt betrayed after the company announced its Surface tablet, a milestone that marked the first time the software giant produced its own hardware. Since then, analysts and other Windows Phone vendors have speculated that Microsoft may release a Surface smartphone at some point in the future. And now we’ve learned that even one of the company’s most loyal partners fears for the worst: In a recent filing with the Securities and Exchange Commission, Nokia (NOK) voiced its concerns about the possibility of a Surface smartphone.

“Microsoft may make strategic decisions or changes that may be detrimental to us. For example, in addition to the Surface tablet, Microsoft may broaden its strategy to sell other mobile devices under its own brand, including smartphones,” the company wrote in the filing. “This could lead Microsoft to focus more on their own devices and less on mobile devices of other manufacturers that operate on the Windows Phone platform, including Nokia.”

BGR exclusively reported last fall that Microsoft was developing a self-branded smartphone that could be released in the coming months. The handset is rumored to be equipped with a display between 4-inches and 5-inches, and will compete directly with other high-end devices such as the iPhone 5 and Galaxy S III.

Dan joins the BGR team as the Android Editor, covering all things relating to Google’s premiere operating system. His work has appeared on Fox News, Fox Business and Yahoo News, among other publications. When he isn’t testing the latest devices or apps, he can be found enjoying the sights and sounds of New York City.