The GPS (Global Positioning System) device in your smartphone doesn't require cell service or internet access to function; that's not how GPS works.
You might not know this because Google Maps et. al. intentionally obscure this fact, to get you to think you need to pay a provider for access or to get you to look at ads in free GPS applications.
This simple Android program (simplegps.apk) shows you your GPS coordinates without requiring any sort of network access. It is open source and free of ads, data collection, etc.