Microsoft’s recent domain registration history has sparked speculation that the company might be planning a partnership with Sony.

The software giant has registered microsoft-sony.com and sony-microsoft.com. Both domains were registered to Microsoft through Corporation Service Company (CSC), a corporate identity protection firm. Forum users at Neogaf discovered the domain names, both of which simply forward to a Bing search result. A great deal of speculation focuses on a gaming partnership between the two firms but it’s likely that the move to register the domains was simply a typical domain protection process. The company has previously registered microsoftinsider.com to protect its brand.

Microsoft could also be planning some type of Windows Phone partnership with Sony Ericsson. A number of images of prototype Sony Ericsson Windows Phone 7 devices emerged earlier this year. Microsoft originally named Sony Ericsson as a launch partner when it first unveiled Windows Phone 7 at Mobile World Congress in 2010. At the time of writing, Sony Ericsson has yet to announce any plans for a Windows Phone device. It has since been reported that the pair could not reach an agreement around Microsoft’s Xbox LIVE integration.

Sony Ericsson had originally planned to launch a 4″ screen device featuring a QWERTY slide-out keyboard. The project was subsequently scrapped but recent rumors suggest that Sony Ericsson may be planning a Windows Phone 7 device later this year. The leaked device, featured below, could hint at Sony’s possible form factor for a future Windows Phone device. Sony Ericsson is a join venture between Sony’s main consumer electronics company and the Swedish telecommunications company Ericsson.

Update: Microsoft’s corporate vice president of Corporate Communications, Frank Shaw, has confirmed that the registration was a “defensive domain hold.”