Many things need a precise time reference, which nowadays often comes from the GPS satellites. AFAIK, the 3G and 4G cell phone standards need precise timing to

Many things need a precise time reference, which nowadays often comes from the GPS satellites. AFAIK, the 3G and 4G cell phone standards need precise timing to work correctly. Which means that "without cell phone reception" is a bit of an exageration; there's always the older 2G GSM standard. Same with the Internet, some networks might need precise timing to work correctly.