CUCM doesnt have a serial number. You need a ESW contract number or try opening with the serial number of the UCS server.
[+5] to George.
You can get the serial number of UCS chassis either from CIMC [the first page which comes when u enter IP on IE] or through vsphere client.
Click on VMHost.Select Configuration TAB ---Hardware -- Processors ---System---Service Tag .
The attached image shows what the output looks like.
the same CUCM serial number can be found in cli
but with this it's impossible to open TAC case becouse spaces not allowed and without spaces also impossible