Summary Box: AT&T posts 4Q loss on charges

HOME OF THE IPHONE: AT&T Inc. activated 7.6 million iPhones in the latest quarter, accounting for one out of every five iPhones sold globally.

STILL DEPENDENT: AT&T had vowed to market competing smartphones, yet the iPhone accounted for about 80 percent of smartphones AT&T activated in the fourth quarter, up from 70 percent just before the vow.

WHY IT MATTERS: AT&T’s iPhone dependency comes at a heavy cost. The phone is more expensive than many other smartphones, and AT&T needs to subsidize each iPhone with hundreds of dollars to put it in customers’ hands for as little as $1.