I don’t have a smartphone, but I used to have Palm m100 (original), and Palm Tungsten E. I did not use it for power point, calendar or anything serious, the main functionality I used is its real player. It got 128 M SD card, so I can store about 30 songs on it.
Today’s smart phone is much more sohpiscated. Besides traditional voice capability, email, messaging (instant, text and multimedia), some phones also got web browsing, MP3/video playback, camera and video capturing, word/excel/power point editing. As I understand some blackberry can do SAP, IBM Lotus, or used as a remote control for home applicance (source: RIM June 25 conference call).