(a) It is unlawful for any person, firm or corporation to intercept or monitor, or to attempt to intercept or monitor, the transmission of a message, signal or other communication by telephone between an employee or similar agent of such person, firm or corporation and a customer of such person, firm or corporation unless such person, firm or corporation does all of the following:
(1) Notifies each employee or agent subject to interception or monitoring that their telephone messages are subject to interception or monitoring.