Some do and some don't. All have the buttons, but unless you can press the button and the GPS comes up, then that particular car doesn't. If the car you're thinking of purchasing doesn't have it, it's almost impossible to add a factory one because the wiring harness is different, so the cost becomes prohibitive.
However, you can get a kit that allows a GPS, among other things, to be displayed on the Prius' display from
http://coastaletech.com/viewtech.htm
coastaletech.com