A location-relevant service system provides location-relevant information to, or performs location-relevant service for, a first mobile unit based on the location of a second mobile unit. In one instance, the first mobile unit is fixed on a vehicle, while the second mobile unit can be provided as a cellular phone. In another instance, the first mobile unit is provided with a display panel, so that authentication can be achieved through providing the display location information to a location-relevant service server using the second mobile unit.