It's been a big month for fixed-mobile convergence--the integration of wireline and wireless networks. The decision now for most businesses is whether to support converged networking on their own or wait for telecom carriers to upgrade their networks. Both approaches have their drawbacks.

Converged networks let people use the same mobile device for both cellular and landline voice calls, via IP access, and switch between the two. By 2011, some 250 million people will make and receive phone calls over such networks and access points, according to ABI Research.

The best option today is to do it yourself. Startup DiVitas Networks last week introduced an on-premises appliance and a client installed on mobile devices to let users roam between carrier cellular networks, company wireless LANs, and public Wi-Fi hotspots. So an employee can start a business call in a car over a cellular network and switch to the company WLAN once he enters the office to reduce cellular charges. "The appliance chooses the most efficient and cost-effective network to connect to," says DiVitas CEO Vivek Khuller. The appliance, which can serve as a PBX or work with existing ones, starts at $5,495.

Siemens Communications this week will introduce a similar appliance and mobile client system, called HiPath MobileConnect, that also lets devices roam between Wi-Fi and cellular networks without dropping calls. The appliance sits between a company's IP PBX and WLAN, extending the office phone to a mobile device. Employees have one phone number and one voice mailbox, whether they're on the road or at their desks. "People don't want to play phone tag when they have important calls coming in," says Luc Roy, VP of product planning at Siemens Communications.

Here's Siemens' catch: Each employee would have to be issued a dual-mode mobile device that can switch between cellular and Wi-Fi networks. The Siemens client is available only on two mobile devices, the Symbian-based Nokia E60 and the Windows Mobile-based Fujitsu Pocket Loox. Siemens plans to support more devices once the appliance becomes available in April, Roy says.

DiVitas says its client works with dual-mode phones, Wi-Fi phones, standard cell phones, and softphones, and it's compatible with the Windows Mobile, Symbian, and Linux operating systems.

MISSING PIECES

Dual-mode mobile devices aren't widely available in the United States. Nokia last year rolled out the E62 business smartphone in the United States, but it doesn't support Wi-Fi.

The BlackBerry, the U.S. smartphone market leader, doesn't come with dual-mode capabilities, but Research In Motion says software it acquired from Ascendent Systems last March is now available on the BlackBerry 8800. The software extends desk phone features to the BlackBerry by connecting over a company PBX and offers wireless-wireline convergence, says RIM. Cisco and Avaya offer similar software, making mobile phones extensions of office phone systems. Hewlett-Packard's new iPaq smartphone recently began supporting the Unlicensed Mobile Access standard, which extends mobile voice and data services over fixed IP access networks.

For businesses to provide fixed-mobile convergence on their own, their networks must support voice over WLANs, the Session Initiation Protocol, and Layer 3 roaming. They must conduct site surveys to ensure adequate network coverage and performance, and deploy wireless and wired quality-of-service and admission control. Security is a big issue, to fend off denial-of-service attacks and identify rogue access points.

The other option is to wait until the telecom carriers upgrade their networks for fixed-mobile convergence, but that's at least a couple of years away. Cingular says it recently deployed the IP Multimedia Subsystem, or IMS, to enable fixed-mobile voice and other IP-based services such as video calling.

This story was modified on Feb. 27 to correct the spelling of Ascendent Systems.