Microsoft released to phone OEMs the Windows Phone 8.1 operating system almost a year ago. Since that time, the company has shipped a number of new handsets running Windows Phone 8.1, as have its various partners.
Windows Phone 8.1 includes support for Microsoft's Cortana digital personal assistant; a notification center; and a variety of new enterprise-focused features.
Denim includes a number of imaging/camera features, including camera quality and speed improvements; a new "Moment Capture" feature for 4K video recording on some of the higher-end Lumia phones; and support for new imaging algorithms, providing for crisper photos in daylight or low light. These imaging/camera enhancements are specifically for Lumia 830, Lumia 930, Lumia Icon, and Lumia 1520 models.
Nokia launched the Lumia Icon exclusively on Verizon in February 2014. The launch gave those of us Windows Phone users on Verizon hope that Microsoft/Nokia and Verizon had begun smoothing out their rocky relationships. But since that time, unfortunately, it doesn't seem like much has really changed.
The news of Verizon's launch of Denim comes just ahead of Microsoft making available the first preview test build of its Windows 10 mobile operating system. Denim is not a prerequisite for Windows 10 mobile, Microsoft officials have said.
For other Windows Phone users still awaiting OS and firmware updates, here's Microsoft's schedule as to when to expect Lumia models on different networks around the world to get those bits. Denim won't be available on non-Lumia phones, but some of the feature improvements in that update will be.