The rumors that Microsoft is developing some kind of phone-like device (perhaps a "Surface Phone" or "Andromeda") have been floating around for years, with little concrete evidence that such a thing exists. But the latest Windows 10 Insider Preview has given new fuel for the speculative fire: it has a set of new APIs for cellular phones.

Windows has had integrated support for cell modems since Windows 8, but this has been restricted to supporting data connections. Telephony—dialing numbers, placing calls—has always required either Windows Phone or Windows 10 Mobile, which has made the full Windows 10 unsuitable for a phone.

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That may be changing. Windows 10 build 17650—a preview of Redstone 5, the next Windows update after the delayed April update—includes some telephony APIs. The new APIs cover support for a range of typical phone features: dialing numbers and contacts, blocking withheld numbers, support for Bluetooth headsets and speakerphone mode, and so on. There also looks to be some kind of video-calling support, suggesting support for 3G or LTE video calling.

Does this mean that Microsoft is going to be making a Surface Phone? On the one hand, there's no smoke without fire. The Andromeda rumors (Andromeda being some kind of a dual-screen device that makes calls but isn't a phone) show no signs of abating, so they likely have some kernel of truth somewhere. On the other hand, these telephony APIs don't appear to be new: they match the telephony APIs already found in Windows 10 Mobile, so their presence in a build of desktop Windows might be nothing more than a mistake (shipping an API package that wasn't meant for the desktop by accident) or the result of some kind of consolidation effort to reduce variance between Windows versions.