I will start by simply quoting from the presentation and letting it speak for itself:
Unified communications (UC) has been the main focus of the VoIP industry over the last few years. And over the last twelve months or so cloud computing has become a big driver of enterprise software. The big transition for UC over the last year was its transition to software. So, if you believe that UC is a software market, and most people believe that, and you believe software is moving to the cloud, then the next step is that UC is moving into the cloud.
You can check out the slides from this Smoothstone / TechTarget webcast by clicking here: Using Cloud Computing to Accelerate Your UC Deployment