Prosecutors say Gambino captain Salvatore Locascio, made member Richard Martino and four mob associates pleaded guilty to charges including money laundering and conspiracy to commit mail fraud.
They face sentences ranging from less than two years to 10 years in prison and they have agreed to forfeit millions of dollars in proceeds from the scheme.
"The perpetrators of one of the largest consumer frauds in history will serve significant time in prison," U.S. Attorney Roslynn Mauskopf said in a statement.
Prosecutors said the men set up shell corporations advertising free services such as psychic readings, phone sex and horoscopes. Calling the numbers, however, triggered unauthorized monthly charges on customers' phone bills, eventually grossing more than $420 million for the Gambino members and their associates.
Prosecutors said Martino was also charged in a scheme that placed unauthorized charges on the credit cards of customers seeking free tours of porn Web sites. Prosecutors said $230 million in fake charges was charged to consumers who believed the sites needed their card numbers to verify their ages.
The head of a Kansas City-area phone company pleaded guilty last month to conspiracy to commit mail and wire fraud for his role in the scheme.