Calling them "Highway ##" is too ambiguous and you're not likely to find any map or GPS that does that.
Having lived in Mississippi, my experience is that most people know the difference between a state highway and a US highway and an interstate and the ones who honestly don't have never traveled outside of the county they were born in and aren't likely to ever need GPS navigation anyway. As time progresses, there are fewer and fewer of those people.
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Via my iPhone 3GS.
Having lived in Mississippi, my experience is that most people know the difference between a state highway and a US highway and an interstate and the ones who honestly don't have never traveled outside of the county they were born in and aren't likely to ever need GPS navigation anyway. As time progresses, there are fewer and fewer of those people.
---------
Via my iPhone 3GS.
State Route and US Route Naming in the USA