UM systems offer enterprise users a common interface for e-mail, voice mail 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 voice-mail systems.

On the scene for almost a decade, UM has been saddled with slow adoption rates. Finally, the technology is seeing an uptick among large organizations, 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.

As is the case with most organizations eyeing UM, interoperability was especially important to the university's technology decision-makers. Seruya and his staff wanted to extend access to unified in-boxes 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 No. 1 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.