A consensus on the definition for "unified communications" may be harder to establish than you might think. For example, here are some possible definitions:

* A unified communications system routes voicemail sent to one or more telephone numbers and faxes to one or more fax numbers into an e-mail inbox where they can be heard and viewed in a manner similar to e-mail.

* A unified communications system routes conventional voicemail, conventional faxes, SMS messages, instant messages, e-mail, VoIP traffic and other content to an e-mail inbox where this content can be viewed using a single interface.

* A unified communications system does all of the above, plus uses a secondary client for initiating Web conferences and other real-time communications sessions.

* A unified communications system provides users with a single e-mail address or other identifier and then intelligently routes content – e-mail, instant messages, telephone calls, faxes, etc. – to one of several clients, including e-mail inboxes, Web clients or mobile devices depending upon pre-determined rules, such as directory roles, time of day, presence status, the priority of the message, the mood of the recipient, etc.

There are certainly more options than those identified above, as well as a variety of nuances to all of these. 

However, the fundamental difference between these options is that the first three are more or less non-selective funnels of multiple data streams into one or a few clients, whereas the last one is more of an intelligent parser of a single data stream into separate streams that are designed to meet the real-time needs of the user. 

Further, the first three represent the current state of unified communications, but the latter represents the long-term future of the technology.

Michael Osterman is principal analyst of Osterman Research.