I'm having same problem!!!!!.
I was able to test this software in Windows and it worked pretty well with issue of not being able to dial out via HT503 on Vonage line. But I prefer to run this on linux OpenSUSE 11.0 so am trying to get it working. I would like to know how to edit these files manually as well.
I was able to get most of this to work by experimentation with manual entries on the files. But I made the MISTAKE of using the WEB INTERFACE to add a second external line. When I chose save this it messed up the configuration files somehow. I will have to attempt to determine what I did but now cannot register with CallCentric. So I'm back to figuring out what got changed by saving the configs.
It would be great of someone at NCH would at least let us know where we can get examples of how to manually create and edit the config files.