Hi Jeff,
I would suggest trying this test:
Call from an FXO to an IP phone. Hang up on the analog phone and stay off hook on the IP phone. If your IP phone doesn't automatically disconnect then you have disconnect problems.
This will manifest itself as stuck ports if someone transfers a call out to the PSTN. Since neither side will be able to initiate a disconnect, the call will stay up.
My first suggestion is to to try 'supervisory disconnect dualtone mid-call' along with 'cptone CN'.
If this doesn't work, making a custom disconnect may be the solution. I wrote a long post on this previously:
http://forum.cisco.com/eforum/servlet/NetProf?page=netprof&forum=Unified%20Communications%20and%20Video&topic=IP%20Telephony&topicID=.ee6c829&CommCmd=MB%3Fcmd%3Dpass_through%26location%3Doutline%40^1%40%40.2cd249ca/3#selected_message
hth,
nick