I disagree with "isn't all that special".

I've worked with it too. It's a PBX/ACD/IVR all in one. That's huge. Get these bundled together from a commercial vendor and you are paying through the nose on a per seat basis. Yeah, it's about as user friendly as Linux in the early days. So if that's not going to work for you, just call Avaya and get out the check book.

From what I've seen the problem is that enterprise managers don't to absorb the risk of using an open source phone system (a highly visible piece of infrastructure).