I believe this is Avaya calling a remote device, like a modem. We have a customer that ported over the number and now it rings when Avaya is doing maintenance or record reconciliation.
This number says it's the "Avaya Malicious Mailbox". Says if you are getting calls with nobody on the line, leave your name and telephone number and they will remove you from the list (?). But it happens over and over and over, like once a year. Its been happening for YEARS.