Killing unlimited data plans has helped make U.S. carriers billions

[Commentary] Killing off their unlimited data plans in recent years hasn't made U.S. wireless carriers very popular in certain circles, but it has helped them make a lot of money off your mobile-data habit.

In the last quarter alone, AT&T reported more than $6.1 billion in revenues from mobile-data plans, while Verizon took in $6.6 billion. Those numbers also reveal significant growth of as much as 20 percent on an annual basis, despite the fact that carriers are adding customers at a slower pace now that most people already have a smartphone. That's because more people are gobbling up more wireless data, and they're also paying more for it as Verizon and AT&T have stopped offering unlimited data to new customers in favor of a variety of tiered pricing plans and overage charges that all add up -- literally -- to billions for the carriers and their shareholders. This doesn't stop the carriers, particularly AT&T, from trying to have it both ways.