You don't use communication tools only in the office or at home - you do so while in the car, in the park, having lunch in a restaurant, and even in bed. Also, there is the fact that businesses are becoming more and more 'virtual', which means a business or its workers are not necessarily confined to one physical office or address; the business might be running with many decentralized elements, most of which exist only online.
Unified Communications takes all of the means by which a modern business communicates – Data, Voice, Messaging and Wireless – and Unifies the experience. This is achieved through the integration of real-time communication services such as IP telephony, instant messaging, video conferencing and Telepresence with non-real-time services such as email, SMS, fax and voice mail.
Unified Communication is not a single product. “It’s a solution based on a set of products unified in such a way as to provide a well defined and consistent user experience across wide range of modern platforms and media types. This means user communicates with one medium and on the other hand the receiver can use another medium to receive the communication (E.g.: voice mail messages through email or a cell phone) for an online user the responses can send immediately via text message or chat or a video call. Otherwise it may be sent as a non real-time message accessible via a variety of media.
How this unification of communication possible? Unification of communication solutions or technologies and product interfaces is made possible by the different of communication "This is not about working 25 hours a day, it’s about eliminating inefficient communications"- Steve Blood research vice president, Garter.