When paramedics have a patient in the ambulance, they're hooked up to a machine which acts as a cell phone. The machine then reads your vitals and the paramedic sends the information to the hospital, giving doctors everything they need to know before the patient arrives.
EMT Eddie Waldrep said, "Our number one concern is patient care, quality of care, and in the long run it's going to be for the patients’ benefits."
The cell phone machines operate using blue tooth technology, the same that most personal use cell phones have, and they use regular cell phone providers. In this case it's Verizon.