The first version was Pocket PC 2000, released in April 2000. It was based on the kernel of Windows CE 3.0 (Handheld PC 2000). Then came Pocket PC 2002, released about two weeks before Windows XP. It was similar to 2000, having full compatibility with Windows CE. Windows Mobile 2003, released in April 2003, was the first version called Windows Mobile. It was software-compatible with Windows CE 3.x and 4.x.
Windows Mobile 5 was released around July/August 2005. It was similar to WM2003, except for a few new additions.
Next... Windows Mobile 6.0 was released in February 2007 and had a kernel powered by Windows CE 6.x. 6.1 in 2008 was much the same, and 6.5, released in 2009/2010, was the last version. It was discontinued in March 2010 and replaced by Windows Phone.
Microsoft ended sale of Windows Mobile devices on June 13, 2010 and ended all support of it on August 21, 2010. Two months later, Windows Phone was released.