The number of 911 calls in Dallas has swollen by more than 17 percent during the last five years, Dallas Fire-Rescue officials said Monday. And while they say there is no cure for the increase, officials believe they have effectively treated a harmful symptom of the problem: EMS "frequent fliers" — people who call 911 several times a month for maladies real and imagined. Many of the callers are indigent and rely on the emergency services for their basic health care needs, such as managing their medications or diabetes-related problems, officials said.