(FORTUNE Magazine) – Tens of millions of people around the world get along quite blissfully with ignorant mobile phones. But here in America, many people want their wireless phones to be smart. In theory, smartphones combine a mobile phone with a personal digital assistant (PDA), allowing the user to make and receive voice calls, browse the web, fetch and send e-mail, exchange short text messages, and store personal information, including contact lists and calendar data.

The trouble is, as Spinal Tap's David St. Hubbins noted, "It's such a fine line between stupid and clever." Some of the earlier smartphone experiments crossed the line into stupid, ran off the shoulder, flipped in the ditch, and burst into flames.

I've been test-driving three new smartphones that stay on the right side of the line, although each weaves dangerously close to the median from time to time. Two are made by T-Mobile USA (the company formerly known as VoiceStream), and one comes from Sprint.

Of the three smartphones, the quirky T-Mobile Sidekick ($200 plus a flat $40 monthly service fee) is the valedictorian with purple hair, the Sprint Treo 300 ($500 plus fees) is the earnest salutatorian, and the T-Mobile Pocket PC Phone Edition ($550 plus fees) is the uncoordinated dork who might have had the highest GPA had he not failed typing and physical education.

The T-Mobile phones suffer from spotty coverage, while the Treo and Pocket PC phones saddle the consumer with complex (and potentially treacherous) service costs.

The most interesting is the Sidekick, the first commercial iteration of the Danger Hiptop unveiled a year ago. T-Mobile says the target audience is 18 to 34 years old, but my experience tells me that the Sidekick will appeal to many geezers over 35 as well. It's the bulkiest of the three, but that's because of the ingenious switchblade-like display screen, which flips up to reveal the best keyboard of any smartphone to date. As a phone, it's tolerable; the Sidekick can be held to the ear, but it works better with a wired earphone. As an e-mail terminal it can't be beat, except maybe by the RIM BlackBerry. (Like the BlackBerry, the Sidekick is always polling for new e-mail.) It also works with AOL's popular Instant Messenger service. (AOL and FORTUNE share the same corporate parent, AOL Time Warner.) Three of the Sidekick's attributes are particularly admirable: a no-nonsense service fee of $40 a month, which includes unlimited data and adequate voice-calling minutes, an intuitive user interface that's ideal for people who are all thumbs, and a server-based storage system that speeds mail handling and prevents data loss, even if the Sidekick itself is destroyed in an X-Games accident.

The Sprint Treo 300, which has a color display under its clamshell lid, is the smallest and most conventional of the three smarties. It's the latest version of the Handspring Treo, and like the Sidekick's, the Treo's PDA functions are based on the popular Palm operating system.

Using Sprint's new CDMA2000 1X network, the most advanced to be deployed so far in the U.S., the Treo handles web and e-mail traffic much faster than earlier wireless handhelds. But don't believe Sprint's hype about so-called third-generation phone network speeds, and beware service plans that can charge as much as $20 per megabyte of downloaded data. Also, unlike the Sidekick, the Treo 300 chokes on mail attachments. The downside of its small size is that the Treo 300 has the worst battery life of the three--about two hours, or half what the others offer--but an optional external battery is said to be in the works. The keyboard is small but usable and has a backlight.

The awkward name of T-Mobile's Pocket PC Phone Edition isn't the only clumsy thing about the first commercial U.S. phone based on Microsoft's mobile operating system. It boasts the best color screen of any PDA I've seen so far, and, as one might expect, it provides the best link with Windows-based PC files. But the big screen also makes the PPCPE too large to carry in a pocket comfortably, and the phone forfeits a physical keyboard for pecking out e-mails and telephone numbers. Instead it relies on pen-based handwriting recognition and a virtual (software-based) keyboard.

The PPCPE is probably the best choice of the three for corporate users, but even so I'd advise waiting for a second- or third-generation Pocket PC phone. There are too many little annoyances in this first version.

Sometimes doing nothing is the smartest thing to do.

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New Crop of Apples

Although its new crop of Macintosh computers is impressive--including the wide-screen, 17-inch iMac ($1,999, above) and the use of dual processors throughout the professional Power Mac G4 desktop family--the juiciest new product from Apple Computer is the Unix-based Mac OS X version 10.2 operating system ($129 if you're upgrading, or free if you're buying a new Mac).

Code-named Jaguar, version 10.2 is as quick as its namesake, leading to generally faster overall computer performance. As a rule, it's risky to upgrade to a new operating system right away, and especially to a version number that ends in a zero. But for those who have been waiting to upgrade to OS X, which Apple says will be the foundation for the Macintosh platform for the next decade, version 10.2 signals that the wait is over. This is especially true for Mac users who find themselves living and working in a Windows-centric world, as 10.2 includes a number of Windows-Mac compatibility advances. Interacting with Windows machines is vital if Apple is to expand its single-digit market share.

One of the more remarkable underlying technologies is Rendezvous, which promises to allow future computers and other information devices to automatically recognize and begin communicating with one another wirelessly. More immediately, version 10.2 has an improved Sherlock search engine, which alone is worth the upgrade fee.