Increasingly, the user interface, or UI of a handset is becoming one of the key differentiating factors for consumers. Users both in the United States and worldwide rank ease of use as one of the most important factors in terms of a phone's features. Handset makers and design companies have heard the message and are designing their user interfaces with that thought in mind. Some of the UI's on Fierce's list have yet to hit U.S. shores, but they pack a lot of promise. Report