Has the telco already provisioned the number?
If not, start with the telco.
If yes, then it would depend on the protocols you use, if H.323/SIP, you might need to adjust your dial-peers.
If MGCP, it all would be done on CUCM.
In CUCM the phone config is exactly the same as any other device, you would need to adjust your call routing if necessary.
HTH
java
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