Had that problem this week. Incoming calls not provided with rings and going directly to the voice mailbox. Using SPA 2102, after hours of testing I had the main portal DID set to CODECS=ALL. I changed it to only G.729u. Then, everything came back on track with only that change. That was on the Montreal2.voip.ms server. Before the change I have made, it was not working on Montreal and Toronto as well. But note that it was working on Atlanta. Codecs seem to be sensitive. Hopefully it's not just coincidence.