Windows Phone (Windows Mobile 6.5)
This logo is only used for smartphones running Windows Mobile 6.5.
Windows Phone 7 Series
On February 15, 2010 the successor to Windows Mobile, Windows Phone 7 Series was announced at Mobile World Conference 2010 by Microsoft.
Windows Phone 7
Due to criticism about the length of its name, on April 2, 2010 Microsoft shortned the name to Windows Phone 7. The circle was changed to green though other colors were still used on occasion.
Windows Phone 7.5
In February 2011, an updated logo was introduced with the Windows Phone 7.5 'Mango' update at MWC 2011. The Windows logo was changed to a square to match the Metro UI used in Windows Phone. The '7' was dropped from the logo.
Windows Phone 8 & 8.1
Starting earlier in 2015 and completed with the release of the desktop version of Windows 10 in July 2015, the Windows Phone brand was phased out, replaced with simply Windows. The operating system is now simply identified as Windows 10 Mobile, using the same branding as the desktop equivalent.