Scroll through the options on the "menu" button on the radio. Speed volume is listed as "speedvol." If it's set to "zero" (0) it won't function, even if it's present.
There's an off chance that if the vehicle didn't come with it "stock," it won't have the wiring harness pin for the speed signal. But given Ford's preference to not stock multiple harnesses, I'd bet it's there, just not used.