That includes the popular Lumia 520, an affordable handset with a respectable feature-set for the money. It's only $29 at the Microsoft Store or $40 from Amazon, both of which represent no-contract pricing. The phone itself sports a 4-inch display with an 800x480 resolution, Snapdragon S4 dual-core processor clocked at 1GHz, 512MB of RAM, 8GB of internal storage upgradeable via microSD, user-replaceable 1,430 mAh battery, 5-megapixel camera, 802.11n Wi-Fi, Bluetooth 4.0, and a few other standard features.
It's not yet known which features will be left out of the mix for lower-end Windows Phone devices, as Belfiore didn't elaborate. However, one would hope Microsoft does a better job this time than it did when rolling out Windows Phone 8 upgrades -- at the time, some older devices were only upgraded to Windows Phone 7.8, which was missing many of the features in Windows Phone 8.
This is also a situation that keeps changing. In November of last year, Microsoft posted to Twitter that there would be Windows 10 upgrades for all Windows Phones devices. Then in January of this year, Microsoft clarified things in a blog post -- "Like any upgrade to a new platform, not every phone will upgrade or support all possible Windows 10 features, and certain features and experiences will require more advanced future handsets."
Hey all: we ARE working on Win10 for 512MB, including 520. Our ambition is to make #Win10 available for these devices but features may vary— joebelfiore (@joebelfiore) February 8, 2015