A quick correction from my talk last meeting. I said that FusionPBX was likely also an Asterisk product, but it is actually based on FreeSwitch (which is a separate product created by one of the originators of Asterisk, but separate from the Asterisk project).
At any rate, still testing. My conundrum is getting a nice system setup and able to be hosted without the fear of hackers getting into my PBX and running up a $400,000 phone bill with my SIP Trunk.
I think the answer lies in a VPN and a hard firewall setup that only accepts the necessary connections over the VPN connection. This way you have a nice secure tunnel through which all of your communication runs, and a secure connection to your capability of calling out. Still researching, but makes sense in my head.