Most phones use
Assisted GPS or AGPS to enhance the satellite signals and improve the startup time for the GPS system. Without the cellular signal to triangulate on known cellular towers the "Autonomous" GPS operation can suffer in locations with poor satellite reception such as in urban canyons and heavily forested areas.
Bottom line, GPS will work, but AGPS works better; so if you are buying a tablet with GPS services as a priority, better get a cellular service too.