To what degree should you be worrying about laying a foundation for fixed-mobile convergence? Gartner Managing Vice President Bob Hafner addressed this issue at the Gartner Enterprise Networking Summit last week in Las Vegas.

Hafner estimated that less than 30% of enterprises will be able to build a specific business case to build or buy a dual-mode Wi-Fi-cellular FMC environment. Rather, he predicted, most enterprises will simply “let FMC happen” over time as cell phones, PBXs, and other equipment naturally get replaced.

Let’s look at some of his reasoning. Hafner noted that free wireless in-building minutes are frequently discussed as a motivator to move to dual-mode - using private Wi-Fi networks for voice calls when in-building, then seamlessly switching to the fee-based cellular network when outside. There’s even talk of eliminating the cost of wired desk phones (and associated cabling) in favor of such phones, as has already been done fairly extensively in Europe. However, Hafner suggested closely examining the near-term savings potential vs. the cost of making a planned move to dual-mode.

“You’ll be spending twice the amount for a [dual-mode] handset that you pay [for cellular-only] handsets today,” he said, though he added that he expects the device subsidy assumed by mobile network operators to remain the same. He added that very few enterprises have built out their private Wi-Fi networks widely enough to support the ubiquitous coverage needed for voice over Wi-Fi (VoWi-Fi)- and that doing so is a costly proposition.

“And the Wi-Fi you put in a year ago is no good for voice,” he said, implying that the roaming and QoS capabilities of even year-old Wi-Fi networks don’t meet the latency and access control challenges of VoWi-Fi - at least not in a standards-based way.

Hafner anticipates that as cell phones conk out, enterprises will figure they might as well replace them with dual-mode phones. When the PBX's life is over, IP PBXs will be put in. Bit by bit, more and more Wi-Fi coverage will be added, said Hafner. He anticipates the whole process taking seven to 10 years.

Joanie Wexler is an independent networking technology writer/editor in Silicon Valley.