Ok, I give up.

I had VOIPo put a trace on my line and they said that they're getting a 404 when they send the call my way. I have scoured (yet again) for information about this error and about getting the server working but it's to no avail.

I appreciate everyone's effort in assisting me with this endeavor, but I've given up and I feel like I've bashed my head against this brick wall for three weeks. The one call I did receive was a false positive and I don't know why I can't get it to work.

Thank you, everyone.