I ended spending weeks trying out the Kazoo platform, and it was incredibly difficult just to install it. Once I had it installed, the monster-ui web GUI was very nice looking, but lacking in functionality as basic as adding a SIP Trunk.
Their IRC channel was very unresponsive, I would often ask the same question every few hours for several days until I get someone to write me back.
Eventually I realized that the single server installation that I spent weeks getting to work was only recommended for development, for production a 7 server cluster was the norm, and running a single server in production was not recommended. I received 2 more recommendations to use FusionPBX so I gave that a try instead.
So far FusionPBX has been great, I was able to get it working with all kinds of features very quickly. The IRC channel is very responsive and helpful. I am planning to roll it out to production soon