Years ago, retailers, bankers and auto dealers had real customer relationships. They knew their customers personally, understood what they wanted, and, as best they could, satisfied their needs through personalized service. As a result, they earned loyalty and a large share of their customers’ business. But this was a costly and inefficient system, and eventually it gave way to mass marketing. Customers traded relationships for greater variety and lower prices.

Today, falling IT costs enable companies to offer both. American Airlines gate agents whom you have never set eyes on know that you are a valuable customer and upgrade you to first class in preference to a once-a-year holiday traveler. Auto dealers remind you when your car is due for a service. USAA sends your daughter information about learning to drive just after her fifteenth birthday, when she is about to sign up for driver’s education. Nordstrom sales reps call you when your favorite line arrives. And Hertz takes your reservation on a dedicated line, then presents you with a waiting rental car complete with your name in lights.

These companies are practising elements of a new approach to marketing...