The convergence of desktop and mobile phones into a single, go-anywhere gadget that works on multiple wireless networks may seem just around the corner; however, real, large-scale deployments are still a long way off, according to IT professionals and vendors at Interop.

The concepts seem simple enough — a Wi-Fi/cellular device that lets you keep talking as you walk out of a building (using a Wi-Fi VoIP network) and into the parking lot (covered by cellular), or vice-versa. Complex hand-off technology between networks, varying standards in handset technologies and a reluctance by carriers to give up billable cell phone minutes to customers with their own VoIP-enabled wireless LANs could present some barriers.

What is known as Fixed/Mobile convergence (FMC), "will be a big plus for end-users, because they'll be able to just communicate," says Craig Mathias, principal of the Farpoint Group, a consulting firm, who led Interop's wireless conference track.

As users move in and out of Wi-Fi and cellular network zones, calls would be passed off among corporate WLANs and carrier cellular networks. "You won't really know what particular network you're using," he says. This will also radically change how enterprise communications networks are built, and the types of services enterprises buy to support them.

"You won't need a desk phone anymore," Mathias says, "or the copper running too the desk, or a pure-wireline voice carrier, or even a PBX."

This potential shakeup of the traditional business/carrier services relationship is where the high-minded concept of FMC meets reality, others say.

"We're still probably three years away before this starts to become a common service," says Alan Cohen, senior director of mobility solutions at Cisco. Right now, carriers are hesitant to help out in this area because there isn't much in it for them, he says. "Moving a call out of the cellular [cloud] and onto a campus Wi-Fi VoIP network takes billable minutes away from the carrier." This will take a huge push from users to get going. A Ford, GM or an IBM will have to start demanding this kind of service on a large scale.

One user who attended Interop this week is ready for fixed-mobile convergence now, but sees little support for it among carriers and equipment makers.