The news comes from Gabriel Aul, an engineering manager at Microsoft responsible for the Windows Insider program:
Wow! We just received our one millionth piece of feedback from the Feedback app! Woohoo! #WindowsInsiders
Windows Insider first launched for testing of Windows 10, followed by a release in January 2015 of the Windows Insider app for Windows Phone. While Microsoft hasn't yet released a full Windows Insider preview of Windows 10 for all Windows phones, the technical preview has been released for several devices so far, and offers a "slow" or "fast" track that allows users to manage how quickly they get releases (and how many bugs they're likely to encounter in the process).
Source: Gabriel Aul