Wireless handheld devices once resided in distinct connectivity camps: 802.11 Wi-Fi or cellular.

That division, however, has started to blur as dual-mode handheld devices hit the market. These emerging products let users switch between wireless local-area network hot spots and cellular links without interrupting service. The advantage is constant access to applications and uninterrupted phone calls as users move between networks.

Although wireless experts say the technology is in its infancy, it merits the consideration of buyers for whom consistent and complete coverage is important. Greg Wilburn, technical sales consultant at GTSI, said products that provide this flavor of roaming may be appropriate for military and public safety customers. He said such customers require high-availability networks.

Vendors have begun marketing products that navigate across communications protocols. Cisco Systems, Proxim — which Moseley Associates is in the process of acquiring — and several other large carriers "are now talking about the convergence of 802.11 and cellular technologies," said Vic Berger, lead technologist at CDW Government.

Berger said this marriage has been somewhat overhyped. But he added that the technology could be useful for people who work in a campus environment, such as on a military base, but often perform their duties elsewhere. In the seamless handoff scenario, a user making a voice-over-IP (VOIP) phone call via wireless could leave the campus and continue the call via a cellular network.

An organization wouldn't have to provide as many phones because the wireless VOIP phone could double as a cellular phone. "A lot of people are looking at that as a tremendous cost savings," Berger said.

Examples of dual-mode wireless handheld products include Hewlett-Packard's iPaq h6315. Developed in conjunction with T-Mobile, the product offers integrated 802.11b and Global System for Mobile Communications/General Packet Radio Service. The product debuted last year and costs about $600.

Motorola's CN620 is a similar product. It is part of a shared development effort by Motorola, Avaya and Proxim.

A couple of server and router products also provide roaming across disparate networks. Cisco 3200 Series mobile routers offer voice, data and video communications across different wireless and wired networks, according to the company. Officials in Cook County, Ill., have tested Cisco's mobile router technology in public safety applications for about two years, said Catherine Maras O'Leary, the county's chief information officer.

NetMotion Wireless, meanwhile, provides Mobility XE, a product that has server and client components. It manages transitions as users roam between networks, according to the company. The Sheriff-Coroner Department in Orange County, Calif., uses NetMotion's Mobility XE on its laptop computers and is investigating its use on smart phones running Microsoft Windows CE, said Ed Lee, a project manager at the department.