But analysts, consultants and vendors have been saying for years that mobile devices, especially the wireless PDAs and smartphones now beginning to gain market share, could be much more, an extension of the enterprise into the field and a major productivity booster - given the right software.

Their customers are finally listening. More and more companies - big and small - are starting to deploy mobile data applications that go well beyond e-mail and Web browsing.

In this first in a multi-part series on advanced mobile applications, we look at who is deploying what and why. In future installments we'll report on the battle for the palmtop - the contention among top mobile operating system platforms such as Microsoft Windows Mobile, Research in Motion (RIM) and Symbian, and among different mobile device form factors.

Yankee Group identifies three broad categories of enterprise mobile applications: already familiar mobile office applications such as mail and personal information management; packaged (but customizable) solutions for processes such as sales force automation (SFA) and dispatch; and built-from-scratch one-of custom applications typically provided by systems integrators or developed in-house.

"Mobile office is still by far the largest segment we see today," says Nathan Dyer, Yankee Group's analyst for the enterprise mobility group. "The second tier is packaged applications for remote access. This is how [network] operators can package repeatable solutions to end users. We're also seeing a lot of that now - for sales force automation and even vertical applications around things like drug store delivery and real estate. A lot of them are being packaged very well, and sold to great success."

Yankee Group is forecasting significant growth in all three segments. It estimates there are 6.3 million users of tier 1 applications worldwide today. That will grow to 21.2 million by 2010. There are 3 million users of remote access and packaged front-office applications such as sales and field force automation. Yankee Group forecasts growth to 10 million by 2010. And it believes the 1.8 million users of highly customized and integrated applications today will grow to 4.7 million by 2010.

William Clark, vice president of research for wireless and mobile at the Boston-based consulting firm Gartner, parses the mobile applications space only slightly differently. His first tier is companies using existing mobile office applications to provide field force automation functions - semi-automating the process of e-mailing field workers information they need, for example. Then there are the packaged and high-end custom solutions already noted.

The latter, in Clark's taxonomy, typically involves significant process re-engineering and integration with back-office systems, including analytical applications. "Companies that can dump a lot of money into development of [these highly customized mobile applications] are few and far between," he says. "It's probably 5 percent of the market or less at this point."

Clark also ranks mobile applications according to anticipated return on investment. The most profitable are what Gartner terms "enterprise field service" solutions. They include dispatch - sending schedules, directions and other information to PDA-equipped field workers over a wireless network. Less familiar are the more proactive capital asset management applications that automate the process of scheduling and wirelessly dispatching field workers to do routine maintenance - of buildings, for example.

"Those are the two areas where there's the highest return on investment," Clark says. "The one because of improvements in customer service and resulting higher retention rates, the other because of the improved return on capital assets."

Some sectors and business operations are more highly motivated than others to deploy these applications. A medical services firm operating mobile MRI (magnetic resonance image) scanning clinics, for example, wants to make sure its vehicles and equipment are kept in top condition and dispatched as efficiently as possible because "every minute of downtime means lost revenues," Clark notes.

One step down in terms of pay-back are direct store delivery applications that consumer packaged goods vendors have been deploying for several years now. They help route sales people optimize their routes, more accurately track inventory in customers' retail outlets to ensure they deliver the right mix of products, and gather information in the field efficiently and get it back to head office quickly.

"What seems trivial is actually extremely important to them," Clark says. "They're looking to shave minutes or even seconds off the process [of visiting each store]."

A "half notch" down in terms of profitability are increasingly ubiquitous sales force automation solutions, which in many cases only requires deployment of packaged applications. They give sales people real time access to critical information about product availability, customer history and allow them to gather information using electronic forms on a mobile device, record transactions and transmit data wirelessly back to the office.

"In this day and age if a sales person doesn't have a BlackBerry or something similar, you kind of question their worth," Clark says. "If you're out on the street, those hours and minutes and seconds really matter. It effects the number of calls you can make in a day, the number of deals you can close in a month."

Most mobile applications generate a return on investment by allowing workers to spend more time in the field with customers or more time on business processes and less time at the office or communicating with the office, Dyer says. Business cases for many mobile applications are "pretty straightforward," Clark adds. If it can be shown to increase sales between 8 percent and 10 percent, that increase will easily cover costs of implementation.

Dyer notes that much of the recent investment in mobile applications has been around improving productivity and increasing revenues. But Yankee Group identifies two other business cases: reducing costs - partly a matter of reducing costs of deploying and maintaining mobile applications themselves by integrating them better - and improving customer service.

"Most of the first wave [of deployments] is around increasing revenues and improving productivity," he says. "But I think in the next wave we'll see a lot more applications and services for decreasing costs."

Do mobile applications really deliver the return vendors and analysts claims?

Clark's colleague, Ken Dulaney, vice president of mobile computing at Gartner, is a contrarian on the question. ROI calculations are inconclusive at best, Dulaney says, because companies rarely go back and check to see if the application actually delivered promised benefits.

"These projects mainly get justified on management emotion," he contends. "Which is fueled by competitive pressures. Or sometimes there's just a sheer will to streamline and automate - it's almost a passion in some companies. There's also often a wear-down factor - a project is pitched over and over and finally management says yes."

This is not to say it's impossible to justify mobile applications on more rational grounds. For one thing, , Dulaney says, they're often not terribly expensive because the mobile devices themselves have come down in price so far. Where mobile applications do most good is filling in "missing links" in supply and information chains that are the lifeblood of every business. Not knowing where a truck is between the time it leaves one location and arrives at another is a simple example.

Eliminating those discontinuities "makes the supply chain faster and more efficient and allows companies to cut down on inventory, and that means more profit and a better top line," Dulaney says. "The trouble is, [these applications] don't deliver benefits in real big chunks. It's a lot of small efficiencies that collectively add up."

The ultimate measure of benefit that companies are looking for is a reduction in labor costs, but it's often difficult to draw a direct line between deploying a mobile application and reducing the work force. The benefit may not click in until far down the line.

For all the excitement growing around advanced enterprise mobile applications - or that vendors are trying build -it's still only a tiny part of the total mobile picture. The wireless PDAs and smart phones needed for most of these applications represent only 16 percent of the installed base of mobile handsets today.

"If you look at the killer app for enterprise mobility, it's still voice," Dyer says. "Over time, though, that's going to shift."

Next time: the battle for the corporate palmtop.