Would AT&T be too big again?

Word that AT&T has agreed to acquire T-Mobile USA for $39 billion has set off alarms in some quarters. There are only four major national cell phone companies, and if AT&T succeeds in absorbing one it will become the biggest player in the business.

Critics worry that the merger will hurt consumers by reducing competition. That could lead to higher prices for mobile phone service than might otherwise prevail. Yet the subscription price of mobile service has fallen since 1999 despite industry consolidation, and local firms provide additional competition.

Is AT&T's anticipated 42 percent market share too big a slice? That's a key question for federal regulators, who should scrutinize the proposed deal under the antitrust equivalent of an electron microscope. A rigorous assessment is vital if the interests of cell-phone customers are to be safeguarded.

Meanwhile, customers old enough to recall when Ma Bell provided rotary telephones can be forgiven for marveling at the extent to which the old is new again. AT&T, after all, was the nation's phone monopoly until 1984, when it broke up under a deal with the Justice Department. Since then, AT&T has had more lives than a cat.

It's unlikely any one company can ever again own the nation's phone business. The question is whether the new AT&T will come too close.