When Ward is in David's apartment talking on the phone with Perry and Casey, Perry has Casey hang up the extension she was on. This was to maintain any attorney-client confidentiality Perry might have with Ward. In most states, a third party hearing one side of the conversation does not necessarily defeat attorney-client confidentiality, depending on what can be heard, but if a third party hears both sides of the conversation, the conversation is not protected by attorney-client confidentiality. If Casey had stayed on the phone, she might have been required to testify about what she heard.