Marie’s Answer: Uncontrollable gossips don’t belong in human resources. By failing to protect confidentiality, this chatty employee damages the credibility of her entire department. So someone in needs to know.
If you fear that her boss will blow off your concerns, seek out a manager with a more sympathetic ear. Then present the facts in a calm, businesslike manner.
For example: "I hate to get anyone in trouble, but I hear a lot of confidential salary information being shared when Mary is on the phone. This seems inappropriate, but I don't think it's my place to tell her. So I just wanted to make you aware of it."
Once you have pointed out the problem, your role is at an end. Management can then decide how to deal with it. For more advice on working effectively with colleagues, check out the topics at Coworker Relationships .