"I'd have to see it to believe it," says Christine Wu, a professor in the Department of Periodontics at the University of Illinois at Chicago, who is on the board of the International Society for Breath Odor Research.

"Is it a gimmick?" says Glenn Clark, a professor at the University of Southern California's School of Dentistry. "Probably. Is it a good idea? Well, it wouldn't hurt."

Bad breath is often caused by bacteria hunkered down on the back of the tongue, but it can also betray problems elsewhere in the body, such as gastrointestinal maladies, liver disease, and diabetes. Anybody who gets a bad-breath bulletin from the Wellness Navigator needs to "follow up and find out what's causing it rather than just buying a bunch of mouthwash," adds Beatrice Gandara, a lecturer at the University of Washington's School of Dentistry.

"I love it that phone companies are getting into the health game," says Ray Browning, a research instructor at the Center for Human Nutrition at the University of Colorado. He cautions, though, that the "phone's downside really centers on its accuracy."

Even if the Wellness Navigator doesn't offer entirely accurate assessments of bad breath or body fat, health experts say that it could still help people track their progress toward health goals.

"Don't focus on the number," Browning says, "but what you're ideally trying to do is change some of these numbers."

Research also suggests that immediate personalized feedback and encouragement like that doled out by the Wellness Navigator can help people achieve health and fitness goals.

"Prompting is critically important, especially in terms of changing health-related behaviors," says John Jakicic, chair of the Department of Health and Physical Activity at the University of Pittsburgh, who has studied the use of cell-phone text messages and wearable monitoring devices in weight-loss programs. "The more immediate you can make it, the better," he says. "I get that feedback, I know where I am."

"The more specific messages are to their target," Jakicic adds, "the more effective they are."