Why is the typical office/IP/VoiOp phone so behind-the-times? [on hold]

Sitting on my desk, and likely on yours too, is one of these:

I will do almost anything to avoid using this device. Checking my voicemail is a nightmare. Logging in and out requires a read-through of the users-manual every time. And, if I ever need to forward a call, I warn the person at the other end of the line that there's a chance the call might not go through. I'm still unsure if I've ever done it correctly.

But my question is: why?

Why are these things still so awful to use? We have seen a tremendous evolution in smartphone interface design: Touchscreens that adapt to the context of a task are commonplace, while cryptic buttons and error codes are supposed to be a thing of the past. We've scrutinized over every interaction on so many different kinds of modern products.

So, why then do office phones lag behind in usability? And, if better designs do exists, why aren't we using them? What is it about this particular industry that keeps office phones in the stone-age?