++May I know which Voice card is getting hung during this time? Is it a FXO card? Please confirm these details.
++Is this issue happening always with any specific FXO card? Please confirm this.
++Is these external calls via FXO ports are taking more time to go back to On-hook state(After disconnecting the call)?Could you please check and confirm this by making a working call(show voice port summary)?
++Is it a new installation?
++Was it working before?
++Is this issue started after any changes done on the system?
++Are you getting the fast busy tone during the time of issue?
++Was this gateway registered to CUCM during the time of issue?
++CUCM complete version.