In part this is because it involves Mr. Slim, 71, whose wealth has turned him into Mexico’s most contradictory business personality. Forbes estimates his fortune at $74 billion, swelled by other interests in banking, infrastructure and mining.
While some Mexicans admire his acumen, others say they believe that his control over the $35 billion telecommunications market has done enormous damage to the economy.
Although prices for many services have come down over the last few years, Mexico’s telecoms still rank among the more expensive of the 34 mostly developed countries in the O.E.C.D., though Mr. Slim argues against the organization’s adjustment for exchange rates.
In broadband penetration, Mexico is at the bottom of the O.E.C.D. table and is falling behind countries like Brazil and Argentina.
Over the years, though, foreign telecommunications companies have mostly given up on Mexico because of the dominance of Telmex and Telcel. Last year, the government auctioned off radio spectrum in a bid to bring a new mobile competitor into the fray, and regulators tried to drum up interest from foreign investors.
“They said ‘Your country doesn’t interest me,’ ” said Mony de Swaan, the president of the Federal Telecommunications Commission, the main regulator.
They complained about the high fees they would have to pay Telcel to complete calls placed to phones on its network and also about foreign investment limits and Mr. Slim. “They said ‘I won’t compete with this gentleman,’ ” Mr. de Swaan said.
Now, Mr. Slim faces a strong homegrown rival. Televisa, the dominant Mexican broadcaster and one of the largest Spanish-language media companies in the world, has been building its own telecommunications network.
Controlled by the billionaire Emilio Azcárraga, 43, Televisa already offers phone and Internet service through its cable subsidiaries. Last month, it bought 50 percent of a small cellphone company, Iusacell, for $1.6 billion.
“You need someone with deep pockets for mobile,” said Jana Palacios Prieto, an analyst with the Mexican Competitiveness Institute. “They are a credible threat.”
Televisa says the government still has far to go to level the playing field. “Decisions that the government should have taken years ago are just being taken,” said Javier Tejado Dondé, Televisa’s director of information, “and they will be challenged in court. So, to say that we have reached a totally pro-competitive moment — I see that as very far off.”
But Mr. Azcárraga and Ricardo Salinas Pliego, who controls Iusacell and who has called for further regulation, have their own history of fighting back against regulation. Between them, they operate a virtual duopoly in broadcast television, more evidence, critics say, of how dominant a handful of powerful companies are in Mexico’s economy.
“What we’re seeing today is the government acting to channel the monopolies, not eliminate them,” said Ernesto Piedras, director of the Competitive Intelligence Unit, a telecom consultancy.
Since February, when Mr. Slim’s companies withdrew all their television advertising, he and the broadcasters have been in open warfare. Both sides ran ad campaigns accusing each other of bilking consumers and freezing out the competition.
That brought a reaction from the authorities.
In April, Mr. Pérez Motta of the Federal Competition Commission announced the fine against Telcel. The ruling argues that Telcel displaces competitors by charging them higher interconnection fees than it implicitly charges itself when it offers its customers free calls to Telcel phones.
Telcel called the commission’s timing opportunistic. “It appears that they are interfering in a dispute between carriers and taking sides in the general argument,” said Alejandro Cantú, general counsel for América Móvil. At the heart of all the disputes are the fees. Almost all Telcel’s competitors say the price Telcel wants them to pay is too high. Over all, these fees cost Mexican consumers an additional $6 billion a year, according to estimates from the competition commission. Mr. de Swaan’s agency has begun setting them at about 40 percent of what Telcel argues it needs to cover costs. The Supreme Court ruling requires the new lower fees to remain in place while disputes wind their way through the courts.
Mr. Cantú said Telcel still planned to contest the new fees.