They have learned that different types of handsets have different levels of quality of service and roaming abilities, Roy said. And in some of the early beta testing the company has done on dual-mode roaming, "a lot of these dual-mode devices perform poorly," he said.

Enterprises also should do a site survey of their premises before implementing a VoWiFi system, he stressed.

Dan Lowden, VP of business development at Wayport Inc, a Texas-based WiFi provider, concurred. "The actual site survey is a critical part of the whole process to ensure you get broad coverage," he said, citing the company's experience in deploying WiFi voice in more than 10,000 locations.

"We have walked into installations done by [enterprise's] own IT groups or other folks and they haven't done site surveys and there's definitely QoS issues," Lowden said.

The chief problem Siemens' customers have encountered has been interference from other sources, he noted.

For instance, one client, a US hospital, was located near an airport, which turned out to have a 2.4 GHz spectrum signal going through one of the hospital's buildings. Another client in Europe discovered its automatic door equipped with a sensor to read employee ID cards also ran at 2.4GHz. "It pays to take a walk," Roy said.

Kathy Small, market managing of mobility solutions at Cisco Systems Inc, said enterprises can work around interference using various directional RF antennas and tweaking power settings to minimize the effect on the network.

Enterprises considering VoWiFi also should understand the way their workers' handsets will be used, said Nate Walker, senior director of product management at Meru Networks Inc, a California-based wireless gear maker.

He said Meru has seen successful installations of WiFi dual-mode phones in Japan. "It requires working with customers to ensure handsets and applications are configured and working correctly," he said.

He added that with most of the installations worldwide that the company is deploying "Data is assumed, voice is planned and location is coming."

Or, as Peter Thornycroft, VoWLAN product manager at California-based wireless gear maker Aruba Networks Inc, put it: "I don't think anyone buys a WiFi network today without knowing it supports voice."

While dual-mode WiFi handsets currently on the market have excelled in providing features required by enterprises, their makers "probably have a bit of a learning to do to" to make more the WiFi feature more practical to companies.

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