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Maxim Voronov

People wait to buy the new Apple iPhone 6 and 6 Plus devices, outside an Apple store in Hong Kong Friday morning, Sept. 19, 2014. The iPhone 6 and 6 Plus were released on Friday in Hong Kong. (AP Photo/Vincent Yu) (AP)

How brands turn customers into devoted followers

Michael J. Armstrong, Maxim Voronov, Wesley S. Helms