The last couple of years haven't been particularly kind to Windows Phone, with plunging sales cuts to to Microsoft's phone businesses.
While Microsoft bought Nokia's devices business with the aim of becoming a big smartphone vendor in its own right, it has now shifted strategy again, and is using its Lumia handsets to showcase the capabilities of Windows 10 to other manufacturers, trying to replicate the success it has had with its Surface tablet PC.
It may be tough to persuade the big smartphone manufacturers to take on Windows 10 Mobile in the short term, but some devices makers are at least experimenting with it.
Here are some of the Windows 10 Mobile devices that are available around the world - from Microsoft and others.
Above - one of Microsoft's most recent Windows 10 Mobile smartphones, the Lumia 950.
HP's Elite x3 phablet is due in the summer, and comes with some impressive specs, featuring Qualcomm's new Snapdragon 820 SoC, 64GB of internal storage and MicroSD card-based storage up to 2TB - plus a 6-inch screen. Continuum - allowing the smartphone to function as a PC by adding a keyboard and monitor - is a key feature for this device. And there's even the option of an additional 'Mobile Extender' - a 12.5-inch laptop-format thin client with no processing or storage capability of its own powered by the x3.
This is Acer's Liquid Jade Primo, a 5.5-inch Windows 10 Mobile, pictured sitting in its dock, which by using Continuum allows the device to delivery what the company says is a "a PC-like experience" when connected to a monitor. Using Continuum the smartphone can be used as a touchpad and virtual keyboard (alternatively a keyboard and mouse can be connected instead). For example users could connect the smartphone to a TV or monitor at at work on one the go - and leave their laptop at home.
It's due to be available in the UK from the end of April, priced from £449.99 including dock.
This is the Vaio Phone Biz - a Windows 10 Mobile device from Vaio (formerly part of Sony), and due to go on sale in April Japan. It boasts a Qualcomm Snapdragon 617 processor and 5.5-inch full HD 1080 x 1920 screen.
This is Alcatel's mid-range Windows 10 Mobile device: it features 5.5-inch HD display, 1.1GHz Qualcomm Snapdragon quad-core processor, 8MP main camera and 2MP selfie snapper, plus 16GB of storage and a 2500mAH battery. However according to CNET it won't support high end features like Continuum and Windows Hello iris security
Spanish smartphone maker Funker has built the W5.5 Pro, a 5.5-inch smartphone with a Qualcomm Snapdragon quad-core processor and 2GB of RAM. The device weighs in at 134g and sports a Gorilla Glass 3 screen and a 2600maH battery and a 13MP camera and costs euro 229.
There are other ways to get Windows 10 Mobile onto your smartphone: users of LTE version Xiaomi's Mi 4 are able to switch to Windows 10 from the standard MIUI Android-based operating system thanks to a ROM developed as part of the Windows Insider programme.
Chinese smartphone maker Umi is reported to be offering a Windows 10 ROM for its new UMi Touch flagship which means that Windows fans can flash the device (which runs Android Marshmallow as standard).
And you don't have to buy a new phone to get Windows 10 Mobile: Microsoft is also rolling out the new operating system to certain smartphones running Windows 8.1. There's a catch though - these older phones don't have the hardware to run some of the most interesting bits of Windows 10 Mobile, like Windows Hello and Continuum. Handsets that will upgrade include the Lumia 1520, 930 (pictured above), 640, 640XL, 730, 735, 830, 532, 535, 540, 635 1GB, 636 1GB, 638 1GB, 430, 435, BLU Win HD w510u, BLU Win HD LTE x150q, MCJ Madosma Q501