Hi Tim,
This feature, which is called "CFA Destination Override" is available in CCM 5.X and CCM 6.x. Have a look;
Cisco Unified CallManager provides a service parameter (CFA Destination Override) that allows the administrator to override Call Forward All (CFA) when the target of the CFA calls the initiator of the CFA, so the CFA target can reach the initiator for important calls. In other words, when the user to whom calls are being forwarded (the target) calls the user whose calls are being forwarded (the initiator), the phone of the initiator rings instead of call forwarding back to the target. The override works whether the CFA target phone number is internal or external.
When the CFA Destination Override service parameter is set to False (the default value), no override occurs. Ensure the service parameter is set to True for CFA override to work. See Service Parameters Configuration in the Cisco Unified CallManager Administration Guide, Release 5.0(4), for information about configuring service parameters.
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Note CFA override only takes place if the CFA destination matches the calling party and the CFA Destination Override service parameter is set to True. If the service parameter is set to True and the calling party does not match the CFA destination, CFA override does not take place, and the CFA remains in effect.
From this CCM 5.1.(1) doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_administration_guide_chapter09186a0080739bb8.html
Hope this helps!
Rob
