To be accurate, Mr5150 said "modern smartphone", which in today's world are iPhones and Android based phones. The Windows Mobile phones (along with Crackberry, Nokias, etc), were the "old" smartphones. They quickly got disrupted by the better, "modern smartphones" - iPhone and Android based phones.
Let's give credit where credit is due. Much like Apple copied and improved on the personal computer interface (the Mac), and Microsoft copied them with Windows, Apple did the same with the mobile device platform. And Google "copied" iOS with Android. Imitation is the sincerest form of flattery.
Google was planning to enter the burgeoning mobile market (before the iPhone was introduced), they bought Android Inc. to compete with Microsoft, Blackberry and Symbian. But when the iPhone came out, it changed the mobile game completely. Google was smart enough to recognize that. They went back to the drawing board and changed their plans and interface accordingly.
Google didn't look at the Microsoft/Crackberry phones and say: "Hmmmm, we should copy that too." No. They knew the iPhone model was better. Even Microsoft abandoned their Windows Mobile phone customers - I was one of them.
I still have my two old Microsoft CE phones. Still charging. With an activated SIM card, it actually still works for calls and texts.
Anyway back to point: Apple's breakthrough wasn't just the new interface without a keyboard. Much more than that (for better and worse):
- smooth, responsive & larger capacitive screen (because they were smart enough to get rid of the keyboard)
- multi-touch (no stylus needed)
- Responsive Internet/Web surfing. Sure, Microsoft/Crackberry/Nokia had that first. But it was painful to use. Nobody really used it for surfing the web.
- a pretty good camera, compared to what was available then. One could argue that the iPhone/Android phones disrupted the idiot camera industry as well.
- Slick MP3/MP4 interface
- probably most important - The Apps. From the Appstore. It changed the way software was created and distributed. Android copied that model too. Hundreds of companies create and sell apps now.
The bad: we have multiple adverse effects and unintended consequences due to the modern smartphone. But that's for another discussion.