Windows 10 Mobile reportedly launching in September
Windows 10 for smartphones will be called Windows 10 Mobile, and it looks like it's not going to be released in the near future. According to Neowin, Microsoft recently held a presentation which included a slide mentioning that "Windows Mobile SKUs will be available late next quarter." Late next quarter (Q3) means sometime in September - so that's when current Windows Phone handsets should be officially updated to Windows 10 (it's not the first time we're hearing about this).
Obviously, phones running Windows 10 out of the box (including the rumored Microsoft Lumia 940, and devices from little known companies - like the Cherry Mobile Alpha Prime) will also not be available before September. Meanwhile, you can install Windows 10 Technical Preview on select Lumia smartphones if you're a member of the Windows Insider Program.
P.S.: What we're seeing above isn't a real Windows 10 smartphone, it's just a reference image used by Microsoft earlier this year.