I been having issue with voicemail ports disconnecting from the call manager. I have 8 voicemail ports configured for one cluster and 8 for the other.
Cisco Unity-CM TSP device 15 (Cisco Unity port 12): Disconnected from Cisco Call Manager
If there are many of these messages in sequence from the same device 15, this port may not be functioning any more. Check to see that it is answering calls, and the server may need to be restarted to activate the port again.
The version of Unity is 4.2 Build 4.2(1)
Call Manager Version is 4.2(3)sr1