CME stores extension info in the running-config/startup-config with all the other router info.
Telnet to the router and do a show run to see if it exists - it will be a construct similar to the following:
ephone-dn 3
number 2032
...
..
It may be that the mailbox number is already in VM - you may need to check the config on CUE by accessing it by first telnetting to CME then putting in:
ser ser 0/1 sess
Where 0/1 is the slot address of your CUE...
Aaaron
Aaron
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