GPS (Global Positioning System) uses US-operated satellites to determine ground device positions. Receiving signals from ~30 satellites and calculating distances from 4+ satellites yields latitude, longitude, and altitude within meters.
For telephony, GPS is critical for emergency call positioning. When calling 110/119 from mobile phones, GPS data is automatically transmitted to emergency services, enabling response even when callers can't provide accurate addresses.
GPS is vital for lost/stolen smartphones. iPhone's "Find My" and Android's "Find My Device" use GPS to locate devices on maps, with remote lock and data wipe capabilities. However, airplane mode or power-off disables GPS, requiring prompt action upon discovering loss.
Privacy concerns exist: location tracking can enable stalking. App location permissions require careful management. See lost smartphone response and phone number privacy.