If a prospective client says something to the lawyer, the lawyer must treat that as confidential information.

I was consulted with a potential client about retaining me. I met briefly with the client and discussed the case. Subsequently, the client chose to hire someone else. I have now been subpoenaed as a witness as to what the client told me. Is this within the attorney-client privilege?

The attorney-client privilege by statute and common laws involves confidences and secrets, but Rule of Professional Conduct 1.6, the rule of confidentiality, is much broader, and it involves anything relating to the representation.