Gail Mills, director of human resources at Home Depot, is a big fan of hotlines. The $66 billion home improvement chain has had a hotline in place for employees and vendors for at least 15 years, she says. "In all that time, the hotline has always paid for itself, because as long as an associate is calling us instead of filing a lawsuit, going to the media, or going to OSHA, it allows us to fix the problem, and that's a huge benefit," Mills says. "It's worth whatever it costs us."

Hotlines may be old hat, but the growing ubiquity of all sorts of media to spread the word, enhanced enforcement against corruption by the Securities and Exchange Commission and the recent Dodd-Frank Act's promise of bigger bounties to whistleblowers are focusing new attention on what used to be just a red phone in the corporate counsel's outer office.

Many companies that haven't had an anonymous way for employees to register complaints or report problems are adding hotlines, with vendors reporting growth rates of 30% to 40% a year. Companies that have long had hotlines are looking at ways to improve them, extend their use to more employees, and expand them to include suppliers and customers. Companies are also gathering and analyzing data about complaints to learn more about systemic problems.