Windows Phone users are understandably a little nervous about the release of Windows 10 for phones later this year. Windows Phone 7 devices couldn't be upgraded to Windows Phone 8, and the fear is that history is going to repeat itself, leaving current Windows Phone 8 handsets, many of which aren't very old, stranded.

Microsoft has, of course, been asked about this. Back in November, the Lumia Twitter account announced "We plan to upgrade all Windows Phone 8 devices to Windows 10 in the future :)"

That was an encouraging sign, but one that earned a little skepticism. Company Twitter accounts, like corporate support forums, are usually staffed by people who lack the authority to set corporate policy or make official pronouncements of this kind. Indeed, those asking for a statement from Microsoft's PR team were told something a little more guarded: "It's our intention to enable a Windows 10 upgrade for Lumia Windows Phone 8 smartphones. At this early stage in the development process, and given the vast portfolio of Windows devices worldwide, we can't predict that all devices will be upgradeable, but it is our intention that the Lumia smartphone line be upgradeable to Windows 10."

The message at this Wednesday's Windows event was once again positive: company staff at the event told us that yes, all current Windows Phone 8/8.1 devices would get Windows 10.

But the story, alas, does not end there. On its Lumia Conversations blog, the company said, "Like any upgrade to a new platform, not every phone will upgrade or support all possible Windows 10 features."

While not having all features isn't too surprising—for example, 4K video recording (currently part of the Lumia Camera app, but likely to be part of the standard Camera app in Windows 10) needs hardware that can record 4K video—the claim that not every phone will be upgraded once again contradicts what we were told before.

Anyone who's been following Windows Phone's development can probably figure out why the messaging is mixed. Microsoft almost surely wants every device to be upgradable, but there are two factors complicating this: OEMs and carriers. OEMs are responsible for some driver and firmware updates, and carriers have to give the go-ahead for every update. As, for example, owners of the Verizon-exclusive Lumia Icon have found out, carriers can drag their feet and introduce long delays in update availability.

Reading between the lines, it's this carrier and OEM dependence that's responsible for the difference in message. The impediment won't come from Microsoft's side; it'll come from those third parties.

However, as is the case today with Windows Phone 8, it's likely that there will be a workaround of sorts. Windows Phone 8 has the Developer Preview program that lets any Windows Phone user install the latest updates to the platform even before their carrier or OEM has approved them. This program is going to be continued for Windows 10, and rolled into the Windows Insider program used for desktop Windows, and it's likely to provide ongoing access to Windows 10 for phone even in spite of carriers.

But Microsoft can't promote this as a way of avoiding carrier shenanigans without upsetting those carriers. That's why the current scheme is named a Developer Preview, and is offered under the pretence of being a way for developers alone to get early access to the software. Many people use the Developer Preview to escape the constraints of their carriers but officially that's not what it's for. The Insider program may well be positioned more broadly, but it'll continue to have the proviso of being "pre-release" and "unsupported" software.