WASHINGTON — AT&T’s wireless business will pay $105 million in penalties and refunds to consumers for unlawfully billing cellphone accounts of customers, the biggest fine yet for such practices, federal and state regulators announced on Wednesday.

AT&T Mobility, one of the country’s largest mobile phone companies, agreed to pay $80 million to the Federal Trade Commission to provide refunds to customers who were billed “hundreds of millions of dollars,” often without their knowledge or consent, for items including ringtones and text messages with love tips and horoscopes, the commission said.

In addition, AT&T will pay $20 million in penalties and fees to 50 states and the District of Columbia and a $5 million penalty to the Federal Communications Commission for the practices, known as mobile cramming.

Even when it was obvious that customers were being harmed, AT&T repeatedly failed to help customers, the F.T.C. said in a complaint filed in federal court in Atlanta.