We're up again, but with longer than normal call setup times. I suspect that an alternate route is now working, and if the primary is fixed soon, this will greatly improve overall reliability.
If you are using MJ software, just run Wireshark on your PC and look at the SIP response packet. If you are using another device, you can either use its debugging features to see the SIP, capture it via a proxy running on your PC, or use a dumb hub or managed switch to snoop the traffic.