Just an FYI.
Neighbor took his Obi2182 from the U.S. to Serbia. The phone has both Callcentric and Voip.MS sip servers configured.
The Callcentric appeared to work fine, but Voip.MS didn't.
The Voip.MS servers were configured for Houston (US) connections and did not connect until we changed to a European server. Normally it would have connected but perhaps with some lag, however there was a change after the somewhat recent denial of service hit many VOIP providers had.
Voip.MS appears to have put Cloudflare in front of their servers. That changes a few things. First it rejects PINGS to IP addresses. It also allows Cloudflare to block what they might consider an attack to the server. It appears that they consider someone outside the U.S. connecting to a server inside the U.S. as an issue, since there are more appropriate servers in Europe.
I understood this might have been the issue when I approached Voip.MS with the issue and sure enough, it was.
I mention this so that should others have registration issues with any SIP provider, they may have also added Cloudflare into the mix to protect their servers. Many providers were attacked and I know a few added Cloudflare to solve the issue.