The authority imposed fines of €1.75 million (US $2 million) on Telecom Italia and H3G and lesser fines of Euros €800,000 on Wind Telecomunicazioni and Vodafone Omnitel.
The authority said it had received numerous complaints from individuals and consumer associations in the course of 2014 in relation to the unwanted supply of costly premium services such as games, videos and music that could be accessed from mobile devices via banners, pop-ups and landing pages.
Customers sometimes found they were receiving the services without their full knowledge and explicit consent and were not furnished with sufficient information on procedures for blocking the services, the authority said.
"The operators derive a specific economic advantage from the marketing of premium services, since they share revenues with the service suppliers, retaining a high percentage of the revenues for themselves," the authority said in a statement Wednesday. The operators were fully aware of the activation and charging for services that had not been requested by their mobile customers, it said.
H3G was ordered to publish an extract of the authority's ruling on its company website and in two national newspapers.
"We investigate on the basis of complaints relating to the Italian market and no information has emerged to indicate that these companies were engaging in similar practices elsewhere," said authority spokesman Giovanni Valentini.
"We're not aware of this type of abuse occurring elsewhere in Europe, although it seems a number of companies have engaged in similar activities in the American market," Valentini said.
Consumer associations welcomed the ruling. "It's time to turn the page," said Pietro Giordano, the president of Adiconsum, one of the organizations that lodged a complaint with the Antitrust Authority.
"As well as paying the fines, the telcos must find, together with the consumer associations, a way to reimburse the thousands of consumers who were forced to pay weekly subscriptions for services they had never requested," Giordano said in a prepared statement.