I checked the Atkins' website - the info there is anything but clear.

From the Atkin's Website:

"rorocigio: Is it true that yogurt has less carbs than the label says because the active cultures eat all the lactose?
Dr. Atkins: The labels on yogurt are every bit as troublesome as the numbers indicate ." - Yahoo Chat - Dr. Atkins on Lowering Cardiac Risk Factors

"Yogurt is just as problematic. Eight ounces of plain, whole-milk yogurt contain almost 11 grams of carbohydrate; the flavored yogurts contain even more." - The Case Against Milk

"The researchers had a group of people with hypertension add extra calcium to their diets in the form of 2 cups of yogurt a day. The idea was that the 800 milligrams or so of extra dietary calcium would help the participants lower their blood pressure. It did—and they also lost an average of 11 pounds over the year the experiment lasted, even though they weren’t dieting and the yogurt added extra calories to their daily intake." - Calcium and Weight Loss