Although Microsoft launched its first handsets with Windows 10 Mobile in late 2015, it took them quite a while to launch it as an upgrade to existing Windows Phone 8.1 users. The upgrade has been in the rumor mill for a few months and Microsoft even unveiled a list of Lumia devices that would get the upgrade some time ago as well. Now, Windows 10 Mobile is finally available as an upgrade to various handsets, including a few non-Lumia devices as well.
The list of phones eligible for the Windows 10 Mobile update is pretty long and consists of a lot of Lumia devices (from Lumia 430 and 435, all the way up to the Lumia 930 and Lumia 1520), as well as the MCJ Madosma Q501 and two BLU handsets - Win HD w510u and Win HD LTE x150q. Strange enough, some handsets that were part of the Windows Insider Program and could run the preview versions of Windows 10 Mobile did not make it to the list yet. Two notorious examples are the HTC One M8 and the Lumia 920.
Unfortunately, the availability of Windows 10 Mobile as an upgrade also varies depending on"device manufacturer, device model, country or region, mobile operator or service provider, hardware limitations, and other factors."