Actually GoogleMaps has an iPhone version of the app. My sisters also have iPhones and I share my location with them through it when I'm traveling to visit them. Then they know better when I'm going to arrive. They also can share their location with me from their iPhone using the googlemaps App. By default it only shares location for an hour or maybe 2 hours. But that can be changed to longer periods, days, months or even until you specifically stop sharing location with them.