So far, wireless VoIP is finding a niche for situations where staff remain within a building. In particular, hospitals, where cellphones are not allowed, have been the site of early adopters (read our recent case studies, Wireless VoIP features win over IT staff and Nurses get the voice-on-Wi-Fi treatment
).

For others, VoIP on Wi-Fi is becoming more popular as it overcomes the technical barriers (What barriers? Read our summary Voice on Wi-Fi? Just say NoM).

Mobile users want voice on Wi-Fi
While roaming within a building might be good enough for staff inside a hospital, salespeople that roam the country also can benefit from wireless VoIP phones and save customers money, says Keith Waryas, an analyst with IDC.

Using VoIP wireless phones or even VoIP softphone software on a wireless PC can turn public hot spots into havens where users can avoid dipping into cellular minutes that may cost a lot of money, according to Waryas.

"Most business users are getting reimbursed by their companies for use of their personal cell phones," he says. So a company would issue a VoIP wireless phone to roving users and receive fewer expense reports for cell phone reimbursement.

A key limiting factor that remains is the number of public hot spots available, although the number is growing rapidly (aarguably, too rapidly for the amount of business).

What about integration?
Even when there are enough hotspots, corporations would have no control over the design and management of public hot-spot networks, so quality could suffer. Also, users would have to carry around two phones apiece - one for Wi-Fi, the other for cellular if they want to stay in range all the time.

Apparently, though, service providers think enough customers will want these Wi-Fi phones to support new services. VoIP service provider Vonage recently announced a service supporting Wi-Fi phones (which it plans to bring to the UK). Net2Phone is about to market a similar service in the US after initiating it in Canada.

Motorola, with partners, is field testing the first dual-mode wireless phones, access points and PBXs (announced last summer) that let users make or receive calls on corporate Wi-Fi networks and continue them on GSM networks as they move out of Wi-Fi range.

So a doctor starting a phone conversation in the hospital via Wi-Fi could walk out of the building, get in a car and drive away [hopefully with a hands-free system - Editor] but continue the call because the network flipped it over to a cellular network.

Systems involving Motorola hybrid phones require use of Avaya PBXs and Proxim access points to coordinate the handoff of calls, and are touted as a way for businesses to save on cellular costs. Businesses would buy the phones and set up corporate cellular accounts, which would let them negotiate lower cellular rates than their employees would individually.

The phones can only tap into specific Wi-Fi networks that must include Motorola presence servers that keep track of where users are.

Service providers can do it
Service providers could offer a managed service based on this technology. Waryas says he expects at least one major US carrier to announce one by summer. This could give users seamless transition from cellular to Wi-Fi at public hot spots.

One hospital telecom manager, who would speak only if he was not identified, is considering the technology and had a concern about billing. He says he'd want to know how the network decides which mode to use and whether there would be a fee for calls received on the Wi-Fi network.

Advocates of this type of service say businesses will be able to negotiate good cellular deals because they will need large buckets of calling minutes. Waryas says he thinks such services will allow for setting up least-cost routing to keep the cost down.
If billing isn't a problem, these dual-mode services could relieve some of the Wi-Fi coverage issues within buildings, Waryas adds. If a user wandered into a dead spot within a building, the call would continue as a cell call rather than drop, he says.