T-Mobile has agreed to pay a $40 million fine to settle a federal investigation into its former practice of faking ring tones when calls couldn't connect in rural areas. The Federal Communications Commission announced the settlement Monday, saying that in the course of the agency's investigation, T-Mobile acknowledged it had injected such false ring tones into "hundreds of millions of calls."

"It is a basic tenet of the nation's phone system that calls be completed to the called party, without a reduction in the call quality—even when the calls pass through intermediate providers," FCC Chairman Ajit Pai said in a statement. "The FCC is committed to ensuring that phone calls to all Americans, including rural Americans, go through."

In the order released Monday, the agency noted it had received complaints from callers and several local telephone companies in rural Wisconsin. The complaints alleged that, though their call attempts had failed, they had nevertheless heard ringing on the other end — prompting suspicions T-Mobile was violating a previous FCC order by prematurely triggering the sounds of a connected phone call in rural areas.

"That is, the calling party believes the phone is ringing at the called party's
premises when it is not," that order explained. "An originating or intermediate provider may do this to mask the silence that the caller would otherwise hear during excessive call setup time. As a result, the caller may often hang up, thinking nobody is available to receive the call."

T-Mobile acknowledged the "oversight" in a statement to NPR on Tuesday, adding that the issue was fixed early last year.

"Our actions have always been focused on better serving our customers and the ringtone oversight, which was corrected in January 2017, was unintentional," the company said. "We have settled this matter — and will continue to focus on our mission to change wireless for good for consumers everywhere."

The company is not the first to be dinged by the FCC for troubles completing calls in rural areas. The agency notes that this is the sixth such settlement.

Not everyone was satisfied with the agreement, however.

Mignon Clyburn, an FCC commissioner, issued a strongly worded dissent to Monday's decision, objecting to what she described as a "severely mismatched consent decree."

For one thing, Clyburn said the fine on the major publicly traded corporation was "dwarfed" by penalties levied on individuals for comparable violations; for another, she criticized the fact that all of the money collected on that fine would be going to the U.S. Treasury and not the actual consumers affected.

"How many times was a loved one calling to check on the wellbeing of an elderly relative, only to have the phone ring and ring with no answer? How many times did a consumer try calling his or her doctor for an urgent refill of an important prescription, only to think that nobody was picking up on the other end of the call?" she asked.

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