Don Dodge writes:
There are several key requirements to make Unified Messaging work. First you need one directory of users across all applications. Active Directory is Microsoft’s answer. Next you need “presence and awareness” of all your contacts available in each application. This means you need to know who is on line and available so you can choose the right communication tool. Once you can communicate and interact across all these modes and devices you need to keep your “state” synchronized. This means that once you have responded to a message, or deleted it, on one device, it should show up as “read” or deleted on all your other devices.
The individual applications have worked fine over the years as stand alone apps. Now they can work together because of common directories, universal presence, and synchronization across devices. Awesome!!