Unified communications, or UC, can mean many different things, depending on where your industry focus happens to be.
In the more collaborative way of viewing unified communications, there's a core set of integrated applications typically built around electronic messaging, inbound fax, and voice messaging from some form of fixed communications. Many of the VoiceCon vendors who showed off more collaboratively focused software would include that core feature set and then add other collaborative applications on top to distinguish their products from the multitude of others on the market.
What the vendors will throw into their collaborative products will of course vary across the vendor landscape. But here's a sampling of what I've seen most recently at VoiceCon.
First, vendors will enhance or integrate their core application offerings such as electronic messaging, fax and voice messaging. Also expect there to be some form of instant messaging (IM). Businesses are starting to learn this can be a very valuable and productive form of communications. It's more direct than email and in some ways not quite as intrusive as a voice call. IM products could be standalone or completely self-contained with more security and more enhanced business controls than current public IM services offer, or else they could be tightly integrated with a broader, UC core applications suite.
On the other hand, sometimes IM offerings are limited to an integration hook into one of the top public IM services. Using a public IM service doesn't allow for as tight an integration and it opens up potential security holes where business use is concerned. Keep in mind this form of IM is supposed to be targeted towards business-specific productivity and not an outlet for employees to communicate with everyone on their personal IM list.
Some UC software has the ability and integration smarts to allow end users to continue using legacy desktop applications such as Microsoft Office. This reduces the end user's learning curve and improves productivity at the same time. Conversely, other UC solutions will provide their own set of custom desktop applications, many of which mimic the functionality of Office. Larger organisations will also have some form of business or operational applications they use on a regular basis. Some UC software will provide various methods for connecting or integrating custom applications into their collaborative suite. How tight that integration is depends on how it's handled architecturally by the UC vendor.