BEWARE of habitual monopolists bearing gifts—especially if they operate in shamefully uncompetitive markets. AT&T’s proposed $39 billion takeover of T-Mobile USA would create a dominant mobile-phone operator, with a 39% market share in America, and a near-duopoly with Verizon, the current market leader: together their combined share would be 70%. It is a mark of the mess that the United States has made of telecoms not just that such a deal is being considered, but also that a duopoly might actually bring genuine short-term benefits. All the same, it would be far better if the Federal Communications Commission (FCC) and the Department of Justice blocked the T-Mobile merger—and tried to reform the market instead.