Wi-Fi/cellular convergence, to let your cell phone call over a WLAN or cellular network, is more complicated: you need a phone that has both cellular and Wi-Fi radios, and a WLAN optimized for voice traffic, not data traffic. A number of vendors, including Agito, DiVitas and Siemens, are offering behind-the-firewall appliances coupled with a smartphone client that enables a seamless handoff between the networks as needed. (Compare Enterprise WLAN products.)

There are early adopters of these products, as well as carrier-based alternatives, such as one from T-Mobile, using the Unlicensed Mobile Access (UMA) standard from the Third Generation Partnership Project. UMA shifts the control functions from an enterprise appliance to a controller in the carrier's network.

But FMC, however defined, comes at a cost, says Paul DeBeasi, senior analyst for wireless and mobility at Burton Group, an IT research firm. "FMC is going to cost money and make the wireless network much more complicated," he says. "You have to become, in effect, a carrier. And you have to engineer your WLAN for a new metric: call capacity."

One complication is the use of personal cell phones for business, says Rob Enderle, principal analyst with Enderle Group, a technology advisory firm. "To scale this up [to the enterprise], you have to create a 'PBX in the sky' and surround it with policies that allow the employee to use the handset for personal and business tasks while automatically and reliably separating the charges accordingly."

Undermining some interest in FMC solutions is the deployment of in-building wireless antenna systems or even femtocells, such as Sprint's Airave service. Both essentially boost the reach and quality of cellular signals throughout a building or a campus. Florida Hospital opted for the in-building wireless system from Mobile Access mainly to improve cellular coverage and performance for physicians, patients and visitors. There was little demand or need for anything more, says Todd Frantz, the hospital's associate CTO. "People don't want their personal cell phone tied into the [corporate] PBX," he says.

For still others, the hype over FMC is just a distraction. "There are simply way too many other, higher priority projects in our queue right now, and there isn't enough of an ROI to bump that priority," says Sam Lamonica, CIO for Rudolph and Sletten, a  general contractor in Redwood City, Calif.