Motorola, Avaya and Proxim are expected to announce a co-developed handset and enterprise network gear that lets mobile phone users roam between cellular networks and wireless LANs. The device, however, will not allow them to roam to public Wi-Fi hotspots (see
New devices prolong the Wi-Fi / cell agony
).

The combination holds the promise of cutting phone costs for business customers and making mobile workers more productive. The Session Initiation Protocol (SIP)-based Wi-Fi/cellular handset, from Avaya and Motorola, is probably the one inadvertently revealed earlier this month. It will be coupled with IP-based or IP-enabled PBXs from Avaya, along with a new WLAN switch and thin access points developed by Avaya and Proxim.

Users are both intrigued and sceptical. Heavily promoted by vendors despite a lack of products, Wi-Fi-to-cell integration faces serious technical problems.

"We have hundreds of house staff who need internal wireless communication at low cost," says John Halamka, CIO at CareGroup Systems, a Boston hospital network. With an Avaya PBX network, Halamka says he is looking into the vendor's Extension to Cellular technology, which lets any cell phone act as an extension of a PBX. But further integration of cellular and WLAN would be more valuable, he says, because staff could use their cell phones for five-digit dialing over CareGroup's WLAN. This also would reduce the electromagnetic interference that signals from cell phones cause.

Another user points to a potential drawback in the cellular/voice-over-WLAN (VoWLAN) technology. "The gotcha is that you have to use the Avaya access point," says David Donoho, senior telecommunications network engineer at the University of Maryland in College Park. "We just put in a bunch of Cisco 802.11 access points, and there's no way we're going to pull all those out just to [deploy cellular and VoWLAN roaming capabilities]."

The university, which has a mixed IP/TDM Avaya phone network, uses the vendor's Extension to Cellular feature. Donoho adds that another issue with the cellular/VoWLAN technology is that only Motorola phones initially would work on the network.

Analysts say the combination of cellular and WLAN technologies will appeal to large companies with many mobile phone users who often rack up big cell phone bills because they use their mobile phones while in the office. "Companies that deploy Wi-Fi networks will soon find out that the incremental costs of adding voice is not that much," sayid Philip Solis, senior analyst with ABI Research. Giving only one device to employees - instead of a cell phone and desktop phone - could be another cost-saving measure. Letting employees have one voice mail box and one phone number also could make workers more productive, he adds.

Avaya, Motorola and Proxim announced their partnership last year. One of the main components of the jointly developed Seamless Mobility product is a Windows-CE-based Motorola phone, which includes 802.11a and cellular radios. The device lets users inside an office make calls from an Avaya IP PBX and Wi-Fi-enabled VoIP network.

Mobile users calling an extension in an office also can roam between their corporate WLANs and cellular networks and have the calls handed off without interruption, Avaya says. Future versions of Seamless Mobility will let users connected to any phone on any network roam between networks without dropping calls, Avaya says.

Software on the phone, written by Motorola and Avaya, lets users dial extension numbers when in an office, as well as access all Avaya PBX features. A SIP stack on the phone supports a push-to-talk feature for connecting to co-workers with SIP-based devices. The software also senses for the presence of Wi-Fi and cellular signals; priority is placed on putting external calls over a Wi-Fi signal because the toll cost of a call made on a PBX generally would be less than a cell phone network charge. If Wi-Fi is unavailable, the phone calls the cellular network.

Avaya's new W110 802.11a access points and W310 WLAN gateway, developed with Proxim, will provide call encryption, fast WLAN connection handoff between access points, and quality of service (QoS) for voice radio signals inside an office.

The new Avaya/Proxim gear uses pre-standard implementations of two IEEE technologies: Wireless Media Extension for QoS support over the air, part of the proposed 802.11e QoS specifications); and 802.11r for fast handoffs of voice connections between access points. The recently approved 802.11i standard is used for wireless encryption and security.

Although the many WLAN aspects of the mobility solution are non-standard, "our intention is to be standards-based," says Fritz Ollom, senior marketing manager with Avaya. He says the mobility technology eventually will be deployable on any company's Wi-Fi gear, supporting the eventual final standard versions of 802.11e and 802.11r.

Another component of the package is Motorola's Wireless Services Manager - software that runs on a dedicated Sun server - which hands off calls between cellular and VoWLAN networks, in conjunction with an Avaya PBX. Sources familiar with the project say AT&T Wireless Services is in trials to support VoWLAN/cellular roaming capabilities with the vendors' gear. Ultimately, AT&T Wireless could offer a plan to businesses in which cell phone users can roam between public cellular and private WLAN infrastructures.

Toshiba, Fujitsu and NEC have announced phones that have both 802.11 and cellular radios, while Cisco has a VoWLAN handset and plans to add cellular technology to it. But these vendors have not developed their respective products in conjunction with corporate network infrastructure partners to support true roaming between networks, says Brian Riggs, an analyst with Current Analysis.

Even for Avaya, Motorola and Proxim, challenges remain, Riggs says. "Many of the important [wireless] technologies needed for this have not been standardised yet," he says, citing QoS, security and fast roaming as examples. He cautions that users adopting the Avaya products would be locked into a proprietary technology.

Another issue is whether enough wireless carriers will be drawn to the technology. "Who gets billed for what? That's still an issue that isn't clear," when a user roams from a cellular network to a VoWLAN running off of a PBX connected to a local exchange. "Someone gains and loses minutes in that equation. How will the carriers be compensated?" BT's Bluephone project which uses Bluetooth for the in-building connection, is the first in the UK to come close to a realistic business model.

Forrester Research analyst Lisa Pierce sees the potential to lock in businesses with corporate contracts as a draw for carriers, even if billable minutes are lost in such a situation. "If such an offering did nothing for (a carrier) but reduce churn, that alone would be worth it," she says.

John Cox and Denise Pappalardo contributed to this story.