One of the most important trends in personal technology over the past few years has been the evolution of the humble cellphone into a true handheld computer, a device able to replicate many of the key functions of a laptop. But most of these "smart phones" have had lousy software, confusing user interfaces and clumsy music, video and photo playback. And their designers have struggled to balance screen size, keyboard usability and battery life.

Now, Apple Inc., whose digital products are hailed for their design and innovation, is jumping into this smart-phone market with the iPhone, which goes on sale in a few days after months of the most frenzied hype and speculation we have ever seen for a single technology product. Even though the phone's minimum price is a hefty $499, people are already lining up outside Apple stores to be among the first to snag one when they go on sale Friday evening.

We have been testing the iPhone for two weeks, in multiple usage scenarios, in cities across the country. Our verdict is that, despite some flaws and feature omissions, the iPhone is, on balance, a beautiful and breakthrough handheld computer. Its software, especially, sets a new bar for the smart-phone industry, and its clever finger-touch interface, which dispenses with a stylus and most buttons, works well, though it sometimes adds steps to common functions.

The Apple phone combines intelligent voice calling, and a full-blown iPod, with a beautiful new interface for music and video playback. It offers the best Web browser we have seen on a smart phone, and robust email software. And it synchronizes easily and well with both Windows and Macintosh computers using Apple's iTunes software.