I'm the quintessential frequent flier, and I've long used the behavior of business travelers on airplanes as a kind of field laboratory for monitoring trends in mobile computing. That's where, for example, I first witnessed in the early 1990s people playing games on their laptops, and in the early years of this decade, people watching rented DVDs on their laptops. It's where I discovered that people would actually watch movies and TV shows on their iPods.

What's currently turning heads aloft now is the BlackBerry Pearl. In the past two months, I've seen a conspicuously large number of impromptu "demos" of the Pearl taking place on airplanes. Someone starts using it, then someone else nearby asks what it is and gets the demo. The Pearl's owner is always rabidly enthusiastic. The other person is always blown away. I haven't seen this kind of enthusiasm on an airplane since the iPod.

I see the BlackBerry Pearl, released on T-Mobile in October and Cingular this month, as the first major fourth-generation mobile phone. First generation: cell phones that didn't feel anything like today's small, sleek, pocket-size cell phones. Second generation: regular cell phones, but small and sleek. Third generation: "smart phones" that combined handheld functionality with the cell phone, but felt like handhelds, not phones. The Pearl is the first major example of the fourth generation: full-featured smart phones that feel like tiny cell phones.

The Pearl, at 4.2 x 2 x 0.6 inches and about 3.5 ounces, is about the size of a closed Motorola Razr -- a "dumb" phone famous for how thin it is.

The Pearl is radical