Whether fixed-mobile convergence is for you in the near-term depends in part on how you define it, but for most, there's no rush.

While a fair number of companies are testing FMC products, few are making large-scale purchases and many aren't expected to for several years at least. On top of that, mobile carriers generally are reluctant to do anything that drains revenue from cellular minutes, so don't look for them to push FMC down your throat.

To step back, it's hard to find agreement on what the term FMC even means, or on how it relates to the even more confusing term of "unified communications". Here, we're talking about FMC in two senses.

The first recognizes that many enterprise users have both a wireline desk phone and a wireless mobile phone, and makes the mobile phone, in effect, an extension of the corporate PBX. The second sense focuses on allowing calls to shift between enterprise wireless LANs and cellular networks: the mobile phone becomes useable reliably within the enterprise, adopts some PBX features, and offloads some mobile minutes to the WLAN.

The vendor white papers on why these are wonderful steps in the evolution of Mobile Man could fill the Library of Congress. One phone number! One voice mail system! Faster response time! Lower phone bills! Improved productivity! Yada yada yada.

And you will find plenty of IT professionals who believe passionately in FMC for precisely those reasons, especially as more phones become available with both cellular and Wi-Fi interfaces. "I don't see FMC yet in large enterprise deployments, but it's getting there," says David Bucciero, director of technical services at Dartmouth College. The college just launched a Wi-Fi/cellular test project.

"Users are saying 'here's my primary device: figure out how to make it work with everything else," says Jack Gold, principal at J. Gold Associates, a research and consulting firm. But these users tend to be highly mobile workers for whom frequent contact with customers or managers almost defines their job.

"Making your mobile phone an extension of the PBX is easy to do," says Craig Mathias, principal for Farpoint Group, a mobile consulting firm. "And it makes an awful lot of sense. For one thing, it gives [mobile phone users] access to the enterprise dialing directory."

Research in Motion has started doing just that, leveraging its acquisition of Ascendent Systems' server application to link the BlackBerry Enterprise Server and BlackBerry smartphones with corporate PBXs. Users get one number that rings simultaneously on their desk phone, a business line at home, or on their BlackBerry. It's done without any other infrastructure changes.

Wi-Fi/cellular convergence, to let your mobile 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.

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.