Had a customer with this system that was installed around mid 1980's. Found programming guide on internet.

Problem, 1 or 2 phones have a MIC button that works when using speakerphone. (Button beeps when pressing it, but doesn't lite up. Also does not work while holding it down).

Checked all the programming options. Switched phones and found the problem to be in the Phone, not in system programming. Customer thinks it was intentionally disabled at one time by previous business owners.

So are the phones (all but 1 or 2) broken or is there a way to enable/disable the MIC in the phone, or is it not even functional in those phones.