Have you noticed that invariably when you connect with someone who answers your call on a cell or mobile phone, you immediately ask, "Where are you?" Whether it is your teenager who is checking in with you, your husband who is on a business trip, or a friend you haven't heard from for a while, you want to know where the person is, so instinctively you ask, "Where are you?"  Inversely if you get a call that originates from a friend who calls you on a cell phone, you are asked, "Do you know where I am?" Knowing this establishes an identity and a personal connection.