UCM - Transfer On-hook

By default, when you are doing a call transfer on UCM, you will press the Transfer softkey on phone to talk to the destination callee, the press the Transfer softkey to complete the transfer.

There is a system parameter in UCM that can change this behavior:
System > Service Parameter > Transfer On-hook Enabled = True

After making the change, when you do a transfer call, after pressing the Transfer softkey, you can put the phone on hook to complete the transfer.