A University of Miami instructor hurriedly checks his voice mail using a laptop to access his e-mail inbox hosted on the school's website. Miles away, the "message waiting" light on his desktop phone is instantly extinguished - a sure sign that the school's traditional and IP-enabled private branch exchange systems have responded to its new unified messaging application.

UM systems offer enterprise users a common interface for e-mail, voicemail and faxes. The technology works by snapping up voice messages, often stored as WAV files; converting these audio chunks to text; and depositing them in a user's e-mail in-box. Usually, the applications also wrap in text-to-speech technology to dump written e-mails into voicemail systems.

On the scene for almost a decade, UM has been saddled with slow adoption rates. Finally, the technology is seeing an uptake among large organisations, thanks in part to an evolving text-based standard: Session Initiation Protocol. SIP lets traditional or mobile phones work together more readily with applications such as e-mail and instant messaging.

"SIP really saves the day, because you can introduce solutions that work not only in the VoIP world but also solve legacy issues as well," says Stewart Seruya, the University of Miami's chief security and network officer.

The key metaphor for interoperabilityAs is the case with most organisations eyeing UM, interoperability was especially important to the university's technology decision-makers. Seruya and his staff wanted to extend access to unified inboxes but were under orders not to rip out major existing systems, such as a huge installed base of Cisco switches. Quickly, the message-waiting light became metaphor for interoperability. "That light was the number one metric we used," says Seruya.

Some vendors and many market analysts tout SIP as an easier way to extend UM across an enterprise without having to swap out extensive infrastructures that connect corporations to public switched telephone networks. Yet SIP isn't the only answer.

Many large communications vendors are still offering UM products based on the ITU's H.323 protocol for enabling IP communication, because H.323 is far more mature than SIP and contains well-defined call-control features.

"Many products now include both H.323 and SIP. So legacy vendors may offer SIP enhancements to their current H.323 platform," says Elizabeth Herrell, an analyst at Forrester Research. Communication heavyweights now involved in SIP deployment include Cisco, Nortel and Avaya, she says.

A maturing protocol SIP is considered less complex than H.323. As the protocol matures, SIP will likely gain ground in the UM market - something analysts are already starting to see, say Herrell and others.

Currently, about 15 percent of major corporations have UM capabilities in place, but another 29 percent are now seriously considering the technology, according to Forrester.

The University of Miami's UM adoption was slower than expected. For years, the school had considered a major voice-over-IP investment, until IT officials decided in late 2005 to buy Communite, a UM/voice-mail replacement system from Interactive Intelligence. Communite's reliance on SIP helped nudge Miami officials into action, and now about 14,000 users have access to UM capabilities, Seruya says.

Other executives have not been so quick to jump on the SIP bandwagon, and they aren't ready to extend UM capability to thousands of users. "We have not found it necessary to make a major move to SIP," says Howie Gold, vice president of IT at House of Blues Concerts Canada (HOB).

HOB organises shows across Canada - not only in House of Blues nightclubs but also in major venues such as Calgary's Pengrowth Saddledome arena - and its travelling production and sales crews use an array of personal communications devices.

"We saw as our benefits from unified messaging things like reduced cell phone usage, because people would not have to call in and check messages," says Gold. "It was also a potential single point of contact for faxes and e-mails." Yet because UM options on voice-mail replacement systems cost about $100 extra per seat, HOB didn't want to blanket the organisation with those features.

Unifying messaging without SIPInstead, a small subset of HOB personnel are offered UM capabilities extended as options on the IP PBX the concert promoter purchased several years ago. HOB has installed Business Communications Manager (BCM) from Nortel. BCM doesn't incorporate SIP, but HOB doesn't need SIP, because its communications infrastructure is built entirely on Nortel equipment. "We are keeping an eye on SIP, because we do think it could ultimately help us lower our bandwidth requirements," Gold says.

While keeping one eye on SIP, HOB officials are focused on the IT budget. "Unified messaging is a bonus for us because it helps us stay far more connected. But it can be hard to justify to the accountants a $15,000 expenditure that provides us with an icon that says you have a new message," says Gold.

Easier to sell, he says, is the VoIP- related drop in long-distance charges for calls between HOB offices in Toronto and Vancouver. Those costs plummeted from $2,000 a month to $250 upon the adoption of BCM.

VoIP investments with limited UM roll-outs are typical, according to IDC analyst Robert Mahowald. For instance, if a business installs a voice-mail replacement system to accommodate 1,000 employees, only a portion of those employees are likely to become UM users. "Nine hundred of them will get vanilla voice mail, and 100 will get unified messaging, which is typically limited to high earners and mobile executives," he says.

Such was the case at Stahls', a manufacturer of imprint graphics used by garment manufacturers to decorate apparel with sports logos and other designs.

"We are licensed for about one-third of our workforce. This is a proper mix for us between travelling, remote and power users who would utilise the features," says Michael Terenzi, manager of IT/telecommunications operations.

Stahls' deployed its UM capabilities through the adoption of a new HiPath 4000 switch and Xpressions 4.0 unified messaging system from Siemens Communications.

Making the market competitiveAs was the case with HOB, SIP didn't play a huge role in Stahls' UM applications. "SIP really wasn't a factor in our decision," says Terenzi. "But I do think SIP will make the market competitive."

Industry analysts such as Herrell and Mahowald agree that the fact that SIP promises to one day knock down the price per UM seat is currently the most attractive aspect of the protocol, which was spun out of the Internet Engineering Task Force (IETF) as a signalling protocol for peer-to-peer multimedia applications.

"SIP may over time help vendors lower their cost structures," says Mahowald. "Since it has been ratified by the IETF, SIP has been generating a buzz. Many enterprises figure if they are buying UM solutions, they might as well be SIP-compliant. But SIP itself doesn't really make a tremendous amount of difference to users right now."

Sean McRae, vice president and chief technology officer at Prudential Northwest Properties in Oregon, echoes that assessment when he describes his company's decision to purchase a SIP-based IP PBX system from 3Com. "SIP played a role in the process, but I don't really think about it. It's transparent," he says.

What companies do think about are the concrete returns on investment available through VoIP purchases - ROI that can be enhanced easily by adding UM options, which are in turn made easier to deploy using SIP. For instance, officials at the US National Institutes of Health Federal Credit Union purchased Interactive Intelligence's Customer Interaction Centre IP PBX, which is based on SIP technology, under the premise that the equipment would yield definitive returns plus 'soft' UM gains.

"We expect to pay for the system in hard costs with the offset of additional maintenance, voice circuits and equipment," says Kirk Drake, vice president of IT. "However, the true ROI, we believe, is in the soft costs and the ability to keep our associates more directly connected to our members."

HOW SIP WORKS 1. User Bob, who works at Acme Inc, requests a session with user Sue, who works at King Corp.
2. Bob's user agent client sends a query to Acme's SIP proxy server on how to reach Sue.
3. Acme's SIP proxy server retrieves Sue's network address from Acme's SIP registrar server.
4. Acme's SIP proxy server sends an invitation to Sue's laptop over the WAN that links the companies and through the King SIP servers.
5. Sue informs King's proxy server that she will accept the message.
6. King's proxy server relays acceptance to Bob via the WAN and Acme's SIP servers and establishes a session.
7. Real-Time Transfer Protocol or media path provides a point-to-point connection .