T-Mobile has agreed to pay a $40 million fine over accusations that the company tried to cover up poor rural cell service with "false rings."

The settlement, announced Monday by the Federal Communications Commission, also requires T-Mobile (TMUS) to implement a "compliance plan" to improve address the issues. The company says it stopped using the false ring tones last January.

False ringtones are used to make is seem like someone isn't answering the phone when in fact the call was unable to go through. This means a person trying to call someone in a rural area with spotty coverage would hear multiple rings and assume the other party was just unable to answer.

"False ring tones also create a misleading impression that a caller's service provider is not responsible if the call fails. False ring tones are a problem on calls to rural areas and are a symptom of the problems of impaired quality and completion of calls to rural areas," says the FCC's order.

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The FCC was investigating T-Mobile for violating rules it introduced in 2013 to improve phone coverage for rural areas. As part of the settlement, T-Mobile will train employees on the rules for rural call-completion, and file compliance reports with the FCC.

"Our actions have always been focused on better serving our customers and the ringtone oversight, which was corrected in January 2017, was unintentional," said T-Mobile in a statement.