I only know of one way to change the term used for an ambulance: have the term used in a popular emergency based show.
Third Watch was referenced earier and gives a prime example. I had never heard that term until that show came on the air. A couple years ago, a guy in Tripoli, Wisconsin (you'll need Google to find it) used the term over the radio. His only connection to New York EMS was his worship of that show. Of course, the next morning his Chief had a few new messages requesting tickets to ride on their new "bus."
While I would never accuse this guy of being a medical professional, regardless of his training, he picked up on the term just like any other viewer. Hell, watch ER so you can see how to defibrillate asystole. Then watch House to find out about all the diseases that aren't Lupis.