I need to tell everybody that trixbox is awesome. A few days ago, I set up a trixbox virtual machine in order to route traffic to a SIP application that wouldn't register correctly with a SIP trunking service.
The configuration was very easy, and after looking at a few blogs because I missed the how to section, everything was up and running. Now, I don't want everyone to think that any idiot can set it up, but it is pretty straight forward and there is a lot of help out there on their forums or other places.
The best thing about it is that it runs Asterisk which is compatible with most SIP trunking services out there as well as SIP devices. It also has a nice clean and easy to use GUI web interface. It makes administering it very easy.
I did run into one bug during my short (so far) usage, and that was logging on to download packages. I had the account set up for the trixbox forums and entered that information into the packages screen and it didn't return any errors or display any success. From browsing around the internet, I found out you have to fill in the registration form for the machine and everything will work.
I will hopefully be replacing our aging PBX system with a trixbox system. Because it is awesome.