I just found an old email about this thread and had forgotten about it because once you read an email, it's no longer highlighted. I felt I should come back to close it.
The problem was unrelated to pfsense completely. What it was is that I had a test SIP system on another network using the same ITSP. When it would register with the ITSP, it would break registrations from the second SIP server, the one I was actually using now.
Once I shut down the original, everything started working again.
Sorry it took so long to come back and explain this and thank you for helping me.