Unfortunately you cannot buy a smartphone w/o buying a data plan.
Actually you can... but you need to buy an unlocked phone, but that means paying full price for the phone which can generally be anywhere from $400 - $700 for the phone. Then you need to buy a 3rd party GPS program which includes the maps a part of the package an that usually costs between $50 - $99. You can then go to a carrier and maybe... maybe they will hook you up with just a voice plan.
In the end, it cheaper to just buy a dedicated GPS device.