One of the favorite topics in the mobile and wireless technology press is predicting the demise of one category of mobile device at the hands of another. Just in the last few weeks, I've "learned" that PDAs will kill laptops, smartphones will kill traditional PDAs, low-end smartphones will kill expensive smartphones, and that a wireless iPod with added PDA features will kill everything.

In fact, we've been hearing these kind of predictions for several years now. The reality is there is unlikely to be any single "killer format", either for consumers or in the enterprise. Individual's priorities and needs differ enormously, and although some formats will be mass markets and others will be niches, at Forrester we expect to see more divergence than convergence over the next few years.

Format Trends
When we look at the different needs of individual consumers, knowledge workers, and field-based workers, we can anticipate a few of the key trends in different formats.

Small, cheap smartphones, mostly based on J2ME, will proliferate. We're already seeing rapidly growing deployment of such devices into field-based jobs in the United States. The devices are cheap, connected, sufficiently powerful to run small yet useful enterprise clients, and double as phones that the worker would often be carrying anyway. These devices are ideal for single-purpose deployments such as time and task tracking but, limited by their small displays and keypads (the devices have to be acceptable as the user's primary phone), they aren't replacements for most knowledge workers, who will continue to rely on more capable PDAs and laptops.

More powerful smartphones that offer a rich PDA experience will blossom among certain knowledge-worker segments. Devices like the palmOne Treo 600 have finally delivered a design that's an acceptable compromise between being large enough to be a PDA and small enough to be a phone, and consequently are proving highly attractive to a certain class of professional. However, their size and cost mean they won't supplant the mass market for phones that are as small and cheap as possible, and especially not in any fashion-driven consumer segments with high replacement rates.

Incidentally, this highlights one popular fallacy among market observers. Because the cheaper kind of smartphone will sell in much higher volumes than expensive, high-end devices, some people are saying that high-end smartphones have "failed" and are doomed to extinction. This is a bit like saying that BMW is in the wrong business because there are a billion bicycles in China. In reality, it's misleading to lump such a broad range of capabilities under the single category of smartphone.

The traditional PDA isn't going away. Low-end smartphones will certainly cannibalize some part of the PDA market among users that just want a simple personal-information-management experience, but anybody who has tried viewing and updating a calendar on a tiny phone screen using a phone's keypad will know that for anything more than read-mostly usage, a PDA has significant advantages. At the other end of the spectrum, high-end smartphones like the Treo 600 will steal away some potential PDA customers, but there's still a significant difference in the way people buy a phone, with its commitment to a monthly subscription, versus a PDA, with its one-off purchase price. Many buyers, both consumers and professionals, still want the smallest possible phone, with the option to carry their PDA or leave it behind, according to need. Others simply want to be able to upgrade their phone and their PDA on different replacement cycles.

Laptops still have an important role, as I've written in previous columns. Ever-improving technology continues to reduce the number of tasks that are dependent on a laptop without good reason, such as projecting a presentation. But until somebody commercializes an organic light-emitting diode screen that I can unfold as needed, I won't be composing this column on any device that doesn't come with at least a 13-inch screen.

Even with all this diversity, there's an as-yet-unmet need for enterprise devices that fall somewhere between a PDA and a laptop or tablet. I've heard numerous enterprises express a desire for something with a larger-than-PDA screen (say, VGA resolution in a format about half the size of a tablet PC), either with or without a keyboard, preferably in a robust package. It's possible that a really well designed device here will be more attractive than PDA or laptop for a lot of vertical enterprise niches. There have been a few attempted solutions in this niche, but nothing has yet reached critical mass; like the smartphone before it, it may take a couple more design cycles to find the sweet spot.

Despite the rush to write obituaries for one format or another, I remain convinced that the market still needs diversity, not homogeneity. I believe that different variants will appeal to different people according to their needs. What works for you will depend on your personal needs as well as your corporate culture, and may not work for your neighbor. Until somebody comes up with a highly flexible, configurable device that's as cheap as a dedicated tool, expect the mobile-device market to show more divergence than convergence.

Carl Zetie is an analyst with Forrester Research.