Here, they're independent, usually hired by a hospital, or employed directly. I guess some of the outlying areas have municipal rescue. I had an ambulance bill for a town I didn't live in, and the bill came from the Town of Yarmouth. Half of it ended up paid with a tax credit.
I live 5 miles from Central Maine Medical Center, and I've never seen a Lewiston ambulance.
You can cross our town in 5 minutes and we only have a small hospital. If anything major happens to you, they have to ship you out to another hospital, usually by helicopter.