What Makes a Smartphone a Smartphone?

We have a large variety of devices out there now. With Windows Mobile, Blackberry, Palm, Nokia, the Iphone, and Google's G1, many would call these smartphones. But as I look around the web I've read that some say devices like the G1 or iphone are not smartphones. Some say they are multimedia phones. When I compare my Dash and my Iphone, there are definitely some differences but there are also many similarities. They both play music, videos, handle all my appointments, contacts, ebooks, bible, internet, email, camera, and so on. So what do you all think? Are all the devices mentioned smartphones? Are some smartphones and some not? Does it matter if the device has a touch screen or not? And of course the real question: What makes a smartphone a smartphone?�*