Ring tones. Phone wallpaper. Horoscope texts. Each billed at a small amount - as little as 99 cents, usually no more than a few dollars - and designed to slip by consumers' limited attention to complex bills.

That's the basic definition of phone-bill "cramming," the time-dishonored practice of stuffing tricky or wholly unauthorized charges onto a bill in the hope that they won't be noticed. And it's what happened for nearly a decade to millions of Sprint and Verizon Wireless customers, according to the Consumer Financial Protection Bureau and other federal and state investigators.

The CFPB, joined by the Federal Communications Commission and attorneys general from all 50 states, announced Tuesday that Verizon, the nation's largest carrier, and Sprint, the third largest, had agreed to pay a total of $120 million to compensate cramming victims and $38 million in fines.

CFPB Director Richard Cordray said the carriers "did not keep a watchful eye" on so-called billing aggregators or the charges they placed on bills, and that both ignored red flags - including lawsuits accusing those very aggregators of cramming.

If the Sprint and Verizon cases seem oddly familiar, there's good reason. In December, fourth-place T-Mobile agreed to pay $90 million to settle similar allegations. In October, AT&T, the second largest, agreed to pay $105 million.

Crammers typically snared victims online.

"Consumers clicked on ads that brought them to websites asking them to enter their cellphone numbers," Cordray said. Some believed they had given their numbers in return for free digital content. "Other merchants simply placed fabricated charges on people's bills without delivering any goods or even communicating with them."

Cordray said the carriers had a financial motive to turn a blind eye: "When consumers paid these illegal charges, Sprint and Verizon were able to take a 30 to 40 percent cut of the gross revenue."

Another sign of their willful ignorance was that the carriers failed to track customer complaints about the crammers' charges, which Cordray called "the most basic fraud-alert mechanism."

Both Sprint and Verizon said in statements that they had taken steps to address the problem before the government's action, including by offering refunds.

"Verizon thoroughly vetted the companies that provided these services and terminated providers who did not comply with our industry-leading practices," a Verizon spokesman said.

One source of wireless-bill cramming was plugged at the end of 2013, when the carriers agreed to quit billing customers for so-called premium text-message services. But Cordray warned that other kinds of third-party billing, such as for mobile wallets, could continue to put consumers at risk.

Under the CFPB's proposed order, Verizon and Sprint would be required to present third-party charges in a separate, clearly labeled section of a customer's bill, and offer customers who dispute fees the option of blocking any from appearing on subsequent bills.

It's worth asking why cramming - an unscrupulous practice that at least borders on the criminal - has persisted for many years. Ed Mierzwinski, consumer program director at U.S. PIRG, sees the answer in the pursuit of the problem by the CFPB, created by 2010 Dodd-Frank financial reforms.

"The FCC not only tolerated cramming for years, it has facilitated it by allowing the carriers to use a variety of incomprehensible line items on bills," Mierzwinski told me. "The CFPB has demonstrated that it will partner with other regulators to protect consumers."

Partner, and perhaps even push them to remember consumer protection is their job, too.

To obtain refunds: Verizon customers can submit claims at www.CFPBSettlementVerizon.com. For more information, call Verizon at 888-726-7063.

Sprint customers can submit claims at www.SprintRefundPSMS.com. For more information, call Sprint at 877-389-8787.