Although I didn't test this solution, if you are running into this issue with voicemail showing disconnected in CUPC and are using HTTPS, port 443, and are connecting to the Unity connection servers by IP address it seems to be caused by the servers self signed certificates. I believe an alternate solution would be to regenerate Unity Connection's Tomcat certificates with an alternate name matching each Unity Connection server's IP address.
From the CLI:
Enter: show web-security
Make note of the following line:
Subject: C=CA, ST=STATE, L=LOCALE, O=ORGANIZATION, OU=ORGANIZATIONALUNIT, CN=COMMONNAME
Use values from above in the set web-security command. Use quotes around items with spaces, ie: replace ORGANIZATION with "My Company" and replace SERVERIP with the IP address of the host you are entering the commands on.
Enter: set web-security ORGANIZATIONALUNIT ORGANIZATION LOCALE STATE CA SERVERIP
Select yes to regenerate the Tomcat certificate
Restart the tomcat service.
Enter: utils service restart Cisco Tomcat
