Hey John,
The only way to force this is to set a "forward no answer" on the phone/DN otherwise
the call will ring until the "caller" hangs up
Here is the way to change this, "System Wide"
Go to Cisco CallManager System Parameters from the Cisco CallManager Administration page. Select Service > Service Parameters.
Select the server to be your IP address and the service to be Cisco CallManager from the drop-down list.
Select Forward No Answer Timer (sec) from the list.
In the Value field, insert the timeout that you would like to configure (the time must be inserted in seconds). The default is 12 seconds so you may want 9.
Click Update on the top of the page.
Note: You do not need to restart the Cisco CallManager service to implement the changes.
From this good "old" (but still applicable) doc;
http://www.cisco.com/en/US/products/sw/voicesw/ps556/products_tech_note09186a0080111c18.shtml#solution3
***This can also be changed on a per Device basis on the Phone configuration page via No Answer Ring Duration = x number of seconds.
Cheers!
Rob
