One of the reasons I use the term "user experience" rather than "user interface" is because the UI is limited to what is painted on the screen and how to manipulate that painting. This is of course an important component, but the full user experience includes more.
In the next set of design patterns, I'll be discussing application management patterns. These are non-UI mechanisms for affecting the user experience. How to purchase and download, cookies, and state management. I should add one on techniques to replicate cookies in a non-cookie environment, but I'll do the Designing the Mobile User Experience
I’m probably stepping on some toes now, but I wouldn’t define it that way.
The user interface of specifically a mobile phones is the display and what’s shown on it, the standard telephony buttons, any other buttons on or beside, the microphone, the speaker etc. Even the aesthetical aspects of a phone are part of the user interface, as they affect how usable the UI is. Include also a display sensitive to sun glare, weak backlight, low contrast on key text, etc.
Even so, I agree with you that user experience is something else. The user interface is the physical “thing” that the user affects and is affected by. User experience is the psychological impressions and reactions.
I agree that the user experience is fundamentally the experience of the user, you raise a good point. The design of teh user experience — at least the parts that can be designed — involves understanding users, researching users, and designing all the things that affect what the user interacts with. As much as possible.