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Phil, what you're saying is true about your phone needing a cell signal to display the maps unless you download the maps (for free) beforehand.
But downloading the maps is no big deal. You can do so up to a few weeks beforehand - say, before you leave home - or even the night before from your motel room (if you've got reliable WiFi there).
I've used an iPad for GPS navigation on trips to Europe. I was able to download the whole of the UK in a few minutes, using Google Maps, and it worked a lot better than a dedicated (paid) nav program I'd used on previous trips.
Just saying.
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