Aiming to supply its track inspectors with a mobile handheld device that would make their job easier and more efficient, major East Coast railway company CSX Transportation chose not a conventional PDA, like a Palm device, or a ruggedized smartphone like a Symbol MC50.

Instead, CSX went with relatively unheralded devices from OQO, a San Francisco-based vendor of ultra-mobile PCs that is attempting to revolutionize the mobile device market.

Rather than beefing up smartphones that run mobile operating systems like BlackBerry, Windows Mobile, or Symbian until they resemble notebook computers in power and performance, OQO has bet on its ability to shrink actual notebooks until they fit into a shirt pocket. The OQO runs Windows XP or Windows Vista and is able to handle full enterprise applications rather than "mobilized" versions of desktop apps. The OQO 02 is slightly larger than a 3-inch by 5-inch index card and is 1 inch deep, meaning it fits comfortably into a jeans back pocket or the inside jacket pocket of a sports coat. It has a 5-inch screen that slides up to reveal a full thumb-keyboard.

"We wanted to go with something small and Windows-based," said Larry Biess, director of advanced engineering for CSX. "The biggest thing for us was, with the OQO we didn't have to develop new software for the handheld device -- we could just port over our existing applications from the desktop environment. It took a lot of pressure off of us."

CSX has 85 contract track inspectors for its 21,000 miles of railway in the U.S. and Canada, and for years they have lugged a pair of 7-inch binders containing specs and manuals and forms for the various assets -- rails, switches, turnouts (where one route diverges into two), and so on. The OQO mini-PCs have Wi-Fi and EV-DO wireless connections but because most of the inspectors work in remote areas most of the synching is done physically once they're back at their stations.

CSX looked at a variety of devices from Motorola's Symbol division, Sony, and BlackBerry-maker Research in Motion, settling on the OQO devices because of the small form factor and the full PC functionality.

The CSX deployment marks a milestone for the budding UMPC category, said OQO senior vice president of marketing and alliances Bob Rosin, as the mobile device company moves beyond a high-end device for well-traveled executives into fieldwork environments.

"In terms of ruggedization, we have optimized the 02 for these environments by enhancing the device with field-ready cases, as with CSX," said Rosin. "That makes it a great solution not only for mobile professionals but field workers as well."

OQO claims to offer the smallest product in the emerging UMPC category, which includes devices from Sony (the UX) and Samsung (the Q1 Ultra) as well as Flipstart, a Paul Allen-backed startup. UMPCs have gotten off to a somewhat rocky start, with Palm's Foleo (a large-screen add-on for the Treo) and Microsoft's Origami getting mostly panned from their intended audience. But UMPC analyst Steve Paine, writing on the Carrypad blog, forecasts that 700,000 of the tweener devices (between a laptop and smartphone) will be sold this year, with that number climbing as high as 7.8 million by 2011. Unlike larger vendors like Samsung and HTC, which produce a portfolio of products to meet a range of needs, OQO will continue to focus on one thing: the pocket-sized PC.

"We are completely dedicated to pushing the frontier for ultra-mobile devices," said Rosin.