Most convergence is really just consolidation: Why hire someone to build a phone system, boardroom execs ask, when you can just pile more work on the IT architect? Why build separate networks for voice and data when a single one can carry both? Why pay phone bills when calls can travel free over the Internet?
Sure, VoIP vendors talk about new applications such as videoconferencing and collaborative document editing, but those are mostly niches. For most organizations, convergence is more about cutting costs than adding new functionality.
But VoIP does offer one compelling feature: Mobility. Unlike a conventional phone line, it can go anywhere where there's Internet access. Employees can receive calls on an office number and access the enterprise PBX while working from home, a hotel room, or if using a softphone, a Wi-Fi hotspot. It's both cheaper to the employer and more convenient to the employee.
Unfortunately for IT, employees have already found an even more convenient mobility technology: the cell phone. While cellular plans aren't as cheap as landlines, let alone VoIP services such as Skype, their coverage beats any tethered technology. Add new features such as push-to-talk or voice messaging, then roll those into GUI-accessible voice mail or centrex, and it's easy to see why people increasingly treat their cell phones as their only phones. To these users, the enterprise PBX--IP or not--is irrelevant.
And voice is just the start. Broadband technologies such as WiMAX will let wireless service providers offer mobile data straight to end-user devices, bypassing firewalls, switches, and servers in the same way that cell phones bypass the PBX.