As Ferro points out, the original value proposition of the PBX is losing its appeal.

The PBX, or Private Branch eXhange, was designed to save a company money. It allowed employees to call other desks in a company without routing the call through the telecom provider’s network. The PBX also made people more productive by allowing them to communicate and collaborate more freely.

Nowadays, how often do you pick up your deskphone and call someone else in your office? Wouldn’t you rather send them an email or an IM or open up a video chat with them?

Heck, I don’t even give out my office number anymore. I hand my Google Voice number and set it to ring wherever I am (office, home, iPhone). The only “value” I get from my PBX is voicemail. And I’d prefer to receive voicemails in my email inbox rather than dial into the PBX.

Ferro points out that the future of the PBX is as a presence server. Rather than routing phone calls, the presence server will tell users whether people are available for a conversation and how you can reach them (email, IM, phone, etc). The server will also hold all your message, regardless of the medium.

Most vendors clearly see that this is on the horizon. See Cisco’s acquisition of Jabber, Microsoft’s Office Communications Server strategy and IBM’s Sametime strategy.

In my view, it’s not a question of if the PBX will go away, but when. Any shift away from the PBX paradigm will lead to a broader and deeper dependence on mobile phones. And mobile phones are still relatively expensive in the United States. I spend four or five hours a day on the phone. If I did all that on my iPhone, I’d blow up my minutes.

So this would require not just a big technological shift, but also a philosophical shift for business leaders. Most enterprises still adhere to the strategic deployment of mobile devices. They hand BlackBerrys to sales teams and top executives and leave the rest of the company tied to their desks.

A world without PBXes would require a big shift in thinking, and this will take time. Have you ever tried to convince the CFO that you need to give the mail room manager an iPhone?