Start-up company DiVitas has launched an appliance that connects dual-mode mobile phones to office Wi-Fi LANs - and leaves control in the hands of the enterprise.

"Businesses want to upgrade, to meet their needs, but they don't want to relinquish control to the carriers," says Vivek Khuller, chief executive of DiVitas. "That idea has no historical perspective." Many fixed-mobile convergence schemes are based around outsourcing phone services to an operator, and these will never take off, for the same reason outsourced Centrex services have never displaced the traditional PBX.

DiVitas Networks is aiming its Mobile Convergence Appliance (MCA) and Mobile Convergence Client (MCC) at organisations that want to free employees from their desks while maintaining control of their IT infrastructure and not being tied down to one carrier. Used on dual-mode Wi-Fi and cellular phones, the products let callers keep talking and using office phone features while they move in and out of range of the wireless LAN.

Most enterprises buy expensive desk phones and PBXs (private branch exchanges) with advanced features, only to have many business calls take place on cell phones, even when an employee is just down the hall. A few handsets can use cellular and Wi-Fi networks, but there have been technical hurdles to going back and forth, and mobile operators have moved slowly on deploying technology that could cost them revenue. For the price of a traditional office phone system, DiVitas said it can give every employee a phone that can be used anywhere.

At the heart of the system is the MCA, which includes the Astrisk open source PBX, and can provide a PBX for a small enterprise or connect to an existing PBX, said Khuller. The MCC software can provide its own interface for presence, showing in real time whether co-workers are available.

Users dial phone call with DiVitas client software, available for dual-mode phones running Symbian (such as the Nokia E61) and Windows Mobile (such as the HTC TyTN or Motorola MC70). In the office this will connect to the MCA over Wi-Fi, and onward to the phone network. Each packet includes real-tine measurements of Wi-Fi and cellular signal strength, said Khuller, so the phone can be switched to cellular when necessary.

To switch a Wi-Fi call to cellular, the MCA first makes a cellular call to the client device that is on Wi-Fi, synchronises the voice signals, and then cuts the Wi-Fi connection. When callers make a cellular call outside the office, the DiVitas client sends an SMS message to the MCA; if Wi-Fi Internet access becomes available - say the user reaches their home network, the client contacts the MCA over the Internet and the MCA switches the call to Wi-Fi.

FMC has been sold on promises of cost reduction, but this is an illusion: "Only 25 percent of employees have their phones paid for by the business," said Khuller. Mobile calls made in the office may cost more, but employees often bear that cost - in reality, the benefit of FMC is increasing control and visibility of calls by bringing them back into the enterprise network. It's an enterprise device talking to enterprise software on the handset, so the IT department can control its own infrastructure, Khuller said.

Most enterprises aren't ready for dual-mode phones, though the technology may make sense for industries including financial services and health care, according to ABI Research analyst Stan Schatt. To really penetrate those industries, DiVitas will have to get its software onto more types of devices, including less expensive ones, because enterprises will want to give the same phone to all employees to realise the system's benefits, he said. A key problem is the lack of support the BlackBerry, he said. DiVitas plans to talk with RIM about cooperation in the future, a DiVitas representative said.

The MCA 1000 can carry to 50 simultaneous calls, enough to support around 250 users - enough to target a significant market size, says Khuller - and can be expanded by stacking multiple units. The cost is around £3000 for the box, including a 10-user client software license. Combining that cost and a £300 phone for each employee the solution is as cheap as an office-based IP phone system, said Khuller - and more powerful.

Stephen Lawson, IDG News Service contributed to this report.