This problem can be observed with any of these symptoms:
Busy tone: By default, call waiting is enabled on the Cisco IP phones. Cisco CallManager returns a busy signal to the caller if there are two calls on the same line appearance and no forwarding destination has been configured or if the forwarded destination is unavailable. Check or configure a forwarding destination for the phone in question. Also check the availability of the forwarded destination.
Wrong destination: The call might reach a wrong destination if the called phone has Call Forward configured and this information is not synchronized with the Structured Query Language (SQL) database.
If this does not resolve your problem, choose from one of these options:
Reorder tone is heard before the complete number is dialed:
If the route pattern that points to the other cluster is assigned to a partition, verify that the calling party IP phone's Calling Search Space (CSS) includes that partition. If it does, try resetting the phone, the partition and the CSS.
If the route pattern is not assigned to any partition, try resetting the gateway associated with the Inter-Cluster Trunk (ICT) if you are using Cisco CallManager 3.2 or earlier. If you are using Cisco CallManager 3.3 or later, try resetting the respective ICT.
Reorder tone is heard after the complete number is dialed:
If you are using Cisco CallManager 3.2 or earlier and the gateway configuration in CallManager 3.2 and earlier or the trunk configuration in CallManager 3.3 or later contains the name of the remote CallManager, try changing it to the IP address of the remote CallManager. There could be some name resolution issues. Changing it to the IP address rules out this possibility.
If you are using any translation patterns for digit manipulation, ensure that the called party is reachable by the calling party. Ensure that the transformation masks match valid directory numbers or route patterns. To understand how translation patterns work in Cisco CallManager, refer to Translation Pattern.
If the called IP phone is in a partition, the most common reason for receiving reorder (Fast Busy) is that the calling party does not have the rights to call the called party. In this case, if the remote Cisco CallManager's gateway and ICT configuration includes a CSS, it must include the partition of the called party.
If any CSS or partitions are used, try restarting the devices in the CSS of the remote Cisco CallManager from the Route Plan menu. Do the same for the partitions and reset the gateway. If no CSS or partitions are used, try restarting the gateway and the IP phone at the remote Cisco CallManager.