(FORTUNE Magazine) – If you think it's a bad idea for people to talk on cell phones while driving, now might be a good time to move to Montana. In November, Handspring plans to begin selling a small digital-phone module that plugs into its Visor handheld computers. When that happens--assuming the VisorPhone module arrives on schedule and works as advertised--people behind the wheel will be able not just to chatter but also to look up phone numbers; send and receive e-mail; grab stock quotes, news headlines and other Web information; check appointment calendars; call up maps and driving directions; play games; and shop online on one pocket-sized device. Come to think of it, now might be the time to consider moving to Suffolk County, N.Y., which recently banned the use of most cell phones while driving.

The VisorPhone module, pictured at right, signals the beginning of what is certain to be a major trend in personal computing: the addition of wireless voice and data communications to handheld devices. Meanwhile, wireless-phone makers are racing to add Internet, data-messaging, and personal-information services to their devices. This collision of products is creating a new category of wireless handheld communicators. Microsoft demonstrated prototypes of its own voice-enabled handheld, called the Stinger, in London earlier this month but said the device would not be available until next year, while Palm Computing said recently it was working with Motorola to create a color-screen phone-computer hybrid for delivery in 2002. Compaq, whose new iPaq handheld has been popular and in short supply since its summer launch, is also exploring a clip-on phone attachment.

But hold the phone: The VisorPhone (expected price $299 when bought with a phone service plan) is, like the Microsoft and Motorola prototypes, based on the Global System for Mobile Communications (GSM) wireless phone standard. GSM covers only about two-thirds of America, and the version VisorPhone uses works on a different frequency from those used in Europe and Asia, so it won't work when traveling outside the U.S. Straightening all this out could prove so annoying that many people may still choose to put up with the awkward juggling act of looking up phone numbers on a personal organizer, like the Visor, and making calls on a separate phone. Another worrisome sign: Handspring declined to make a VisorPhone unit available for testing, saying it was too unreliable for a formal review. That is not encouraging for a product the company plans to put on the market in a few weeks--especially given Handspring's past difficulty in delivering other promised Visor modules.

Nevertheless, in demonstrations at a recent wireless communications trade show, the Visor with VisorPhone attachment appeared to work as intended. So for business travelers and others who want to carry only one device, it may well be just the ticket. The phone module contains a small speaker, while the microphone is built into the Visor. A small headset plugs into the module, and the user can manage calls with the Visor's touch-sensitive display screen. Because the Visor contains the user's contact files, everyone he or she normally calls is already on a speed-dial list.

Handspring did let us test its two new Visors: the Prism ($449), its first color-screen model, and the Platinum ($299). Both are worthy of consideration, primarily because of the innovative Springboard expansion slot that Handspring builds into each Visor. The slot sets Visors apart from other handheld computers and allows the addition of special-purpose modules like the VisorPhone. One such module is the new Good Technology SoundsGood MP3 player ($269), which stores an hour of digital music that can be transferred to the device through a Windows USB computer.

The new Visor Platinum is notable for its fast Motorola Dragonball processor and its ability to display 16 shades of gray. The Platinum, being platinum-colored, is slightly better looking than earlier, black Visor models. But it is still clunkier than the elegantly designed aluminum Palm V, the most popular handheld organizer on the market. Sony's Clie (pronounced KLEE-ay) is a skinny, Palm OS-based handheld with eight megabytes of memory. The Clie ($399.99, a buck more than Palm's comparable Vx model) also has an expansion slot, but one based on Sony's Memory Stick technology. While Memory Sticks are handy for adding memory and software, it remains to be seen whether developers will come up with innovative hardware add-ons for the Clie.

The Visor Prism, Handspring's first color-screen device, finally matches rival color models from Hewlett-Packard, Palm, Casio, and others. The Prism's backlit screen does a decent job of displaying digital photographs and color maps. The Prism has a rechargeable battery that's good for only about one day, but it recharges in less than 20 minutes. Its better color screen, faster processor, and greater expansion capabilities make Prism a hands-down winner over Palm's color-screen model, the IIIc ($399).

While Visors use the Palm OS operating system, Hewlett-Packard, Casio, Compaq, and others use the Pocket PC operating system, a stripped-down version of Windows developed by Microsoft. Unlike Visors, which are designed for simplicity, the color-screen Pocket PC models try to do many things without add-ons, from handling Microsoft Office files to serving as MP3 players, voice recorders, and e-book readers.

Compaq's iPaq H3650 ($499.99) is definitely the one to beat in the Pocket PC category. It is the thinnest and lightest color-screen handheld. With an optional expansion pack, it can connect to wired or wireless networks. In fact, the iPaq's screen is so bright in comparison with the notoriously dim Palm screens that when iPaq users see a Palm user struggling to read the display, they cheerfully offer their iPaq screen as a flashlight to help out.

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