[Dalberg-Acton]

Microsoft Windows Mobile 2003 was the earliest I know of, I had one. Apple started development on the iPhone the following year.

[dayglored]

You're right about Mobile 2003 -- the precursor to Windows Phone. I was thinking of the latter when I said they came late to the party (2010).

Microsoft clearly wanted early Mobile to be a Windows computer in your hand, with as much desktop functionality as could be squeezed into a handheld at that time. WinCE with a Windows file system, even.

Unfortunately, that's not what mobile devices were or are about -- they are media consumption devices, gaming, social media, and BTW a cell phone. It took the iPhone to bring that concept screaming into the general consciousness, and Microsoft pooh-poohed it (see famous video interview with Steve Ballmer deriding the iPhone).

One might argue, of course, that Apple saw the error of Microsoft's ways with Mobile, and benefited from that in creating the iPhone, but they already had the iPod etc. to work with and had seen the future.