If you still own the Yezz Billy 4.7, you're now free to install Windows 10 Mobile Insider Preview builds on it. The Windows Device Recovery Tool was recently updated to support the device.
Activision acquisition, forced updates, and Google Play on Windows
Dev channel build adds “Jenny” and “Aria” to Narrator, visual tweaks and more fixes
windows 11 insider preview
Billy 4.7 RSS
Microsoft has rolled out its latest update to the Windows Device Recovery Tool, bumping it up to version 3.7.18601 with support for four more handsets, including the VAIO Phone Biz and the NuAns NEO.
Yezz, which has launched three Windows Phones in the last year, confirmed that it will upgrade those devices to Microsoft's latest OS this fall, with new Windows 10 Mobile handsets on the way.
One of the many new manufacturers to sign up to Windows Phone will formally launch what it claims is the world's "slimmest and lightest" handset running Microsoft's mobile OS at IFA this week.