Hi,
Yes you can do this, if you are using H.323 you can use a voice translation rule to mask the number before getting to CUCM, if you are not using H.323 you may create a route pattern and disable the CLID on the calling party options, this way you will not reach the DN directly but the RP (you may do this by partitions and CSS) then the RP should be able to reach the phone.
The easiest way would be to set this up on the H.323 GW
Hope this helps, if you have any specific questions let me know.
Christian Nuche
PDI HD