You are connected directly to the telco's gatekeeper or do you have an onsite gateway that connects to the telco's gatekeeper? If you are connected directly to the telco's gatekeeper, they will have to provision the new dialplan for the new DID range to point to your CUCM. At this point you should be recieving what ever digits their sending you (4,5,7,10, etc) and translate them accordingly. Or build the CUCM dialplan (DN's, CTI route points, etc) to match the recieved digits.
Hope I understood your question correctly.