The long courtship of Wi-Fi and cellular phones took two teasing steps towards the altar this week, but stopped short of consummation. Two devices were launched that combine the technologies, but neither does voice over public Wi-Fi. The combo Wi-Fi phone from Motorola does voice over Wi-Fi but doesn't support 802.11b, while the HP iPaq supports 802.11b but doesn't do voice over Wi-Fi.

On Tuesday, as expected, Motorola introduced its CN620 phone, which acts as a voice-over-IP (VoIP) phone on Wi-Fi networks and a cell phone on GSM cellular networks. Handoffs between the two networks are handled by technology developed by Avaya and Proxim. The CN620 can also handle data communications on both networks. However, it only supports 802.11a, on the grounds that this is better for supporting voice in office WLANs.

On Monday, Hewlett-Packard introduced an iPaq handheld computer that works as a voice GSM phone, and can roam data calls without dropping a signal between 802.11b Wi-Fi hot spots and GSM cellular services, choosing the best option. T-Mobile announced a service to support this on its GSM cellular data network in the US.

However, the device does not not come with voice over IP software. This could obviously be added by third parties, as pointed out by the Financial Times, but T-Mobile isn't rushing to support voice handoffs between its Wi-Fi and GSM networks. When asked, Rick Roesler, HP's vice president of handheld marketing, hedged, saying HP and T-Mobile view a combined Wi-Fi, VoIP and GSM phone as a "very interesting" possibility.

What do businesses want?
Motorola, HP and T-Mobile are all aiming their new combo phones at the enterprise market, and their public statements are all about how well they are doing that.

The CN620 is part of Motorola's Enterprise Seamless Mobility suite of products, which includes a WLAN gateway jointly developed by Avaya and Proxim. The gateway acts as a switch controlling the access points and a communications manager from Proxim. The communications manager moves incoming phone calls from wired local and long-distance networks to the IP network, turning circuit-switched calls into IP-based traffic.

Ed Zander, chief executive of Motorola, said in a statement that the Enterprise Seamless Mobility product line "will change the notion of work. Work will no longer be defined as where you are, but as what you do and how you do it. One device, one phone number, one voice mail - and the key functionality of your office desktop - on a single mobile device."

HP's Roesler said the new iPaq 6315 was developed to take advantage of a back-end enterprise infrastructure designed to support handheld devices as well as the proliferation of corporate Wi-Fi networks.

The Motorola enterprise mobility product line is designed to support easy handoffs of calls between Wi-Fi and GSM networks, with built-in intelligent routing through a gateway. This allows the CN620 to act as an extension of an enterprise private branch exchange, with all the features and functions of a wired desk phone.

Why use 802.11a?
Motorola chose to use 802.11a, in the 5GHz band, instead of 802.11g in the 2.4GHz band, although both offer the same theoretical speed (54 Mbit/s), and 802.11g would allow the device to fall back to the more common 802.11b standard and be used in public Wi-Fi hotspots. The reasons given for this decision are that 802.11a has more channels, less likelihood of interference from other devices (particularly other Wi-Fi networks), and better quality of service, which is useful for voice.

It is true that some of the objections to voice on Wi-Fi do not apply so strongly to 802.11a. However, it has plenty of problems of its own.

A Motorola spokeswoman said enterprises that don't have an 802.11a network would need to install one to support the CN620. They would also have to purchase supporting hardware, such as the gateway. Enterprises aren't so price-conscious as other users, perhaps, but in a smaller market 802.11a kit is not subject to the same economies of scale as 802.11b/g.

Craig Mathias, an analyst at Farpoint Group, said he is "surprised" the Motorola phone uses the 802.11a protocol, but said he expects enterprises to eventually install tri-mode Wi-Fi networks, which support all three 802.11a/b/g standards.