Companies can now buy a service that automatically analyses phone calls made by office staff, figures out which are for business and which are personal, and delivers a monthly list of repeat offenders directly to top management.

"If you're making a 30 second call every morning at about 9 a.m. and the number doesn't match those used by your colleagues then we can guess fairly accurately that's your spouse," said Robert Picton, product manager at South African IT firm Dimension Data.

Picton says that although other IT companies offer call analysis technology, Didata is the first to translate that information for managers, without requiring staff to use passwords -- a system he says is open to abuse.

Didata says a company can cut its phone costs by 10-15 percent by using the 'Guardian' monthly service, not to mention hours of manpower saved through increased productivity.

Employees might bristle at the thought of managers monitoring calls. But Didata says the system focuses only on those who run up huge bills or spend hours of work time on personal calls, and says no one listens in to the calls themselves.

"Obviously it is acceptable to make a few calls home," said Picton. "But this is about the minority who are spending 12 hours a month on the phone for non-business purposes and running up bills of 800 rand ($114.7).