Enabling Barge and Single-Line Barge
To enable Barge (not cBarge, which uses conference resources), the built-in bridge must be enabled. This is set globally (CallManager Service parameters) and overriden at the phone. The default is for the built-in bridge to be disabled.
From a user perspective, to activate the remote-in-use state, when a shared line is in use on Phone A, the line on Phone B will indicate that a call is in place. Assuming Single-line Barge or Single-line cBarge are disabled, pressing the shared line on Phone B activates the Remote in Use state (the default Single Line Barge setting is Off). Barge can then be selected. Privacy is important - if Privacy is enabled on Phone A, Barge can not be enabled.
Single line barge is controlled using CallManager Service Parameter, Single Button Barge/CBarge Policy. To verify Barge is working, first leave Single Line Barge at its default (off) and, once Barge is working with the Remote-in-Use state, enable Single Line Barge (if desired).