The price competition among mobile carriers has been driven by a divide between the two smaller carriers and the two larger carriers. The larger companies have higher profit margins because they can spread the cost of a national network across a larger customer base, allowing them to pocket a larger portion of each customer’s monthly payment. T-Mobile and Sprint are under pressure from investors to match those profit margins, and the only way to do that is to get bigger. But if the industry is reduced to three companies of roughly equal size, they will all be able to post similar profit margins, and the pressure to compete for market share will dissipate. What results from this could well resemble the airline industry, where four fat companies dominate the domestic market, largely avoiding the pain of price competition or the pressure to improve service.

There is little realistic prospect that the national mobile phone companies would face new competition. There are small mobile companies, including some with wealthy backers like Comcast, but a new national competitor would need to either build a network of phone towers at vast expense or rent the use of someone else’s infrastructure, a model that has worked in Europe but would require a new approach to regulation in the United States.

T-Mobile argues that the deal will make it a more formidable competitor, able to increase its investment in technology — particularly the costly build-out of a next-generation “5G” network that promises to allow evermore data to move through the ether at high speed.

But T-Mobile can make those investments on its own. Indeed, it may be more likely to do so. There is growing evidence that corporate concentration reduces investment and innovation, by reducing the incentive to stay ahead of competitors. A 2016 study that surveyed a decade of manufacturing mergers found no sign of productivity gains. The International Monetary Fund estimated in Apri l that the increase in corporate concentration since 2000 contributed to a decline in investment that reduced economic output by about 1 percent in the average advanced economy. It warned that continued concentration could increase the impact.

Corporate mergers also are holding down wages. Workers lose leverage when the number of potential employers is reduced. The effect may be greatest for those with specialized skills, but an analysis by the liberal Economic Policy Institute estimated that even workers in mobile phone stores could see a 1 percent to 3 percent decline in their wages.

A key reason for the creation of antitrust laws was the desire to limit the political power of corporations. Mobile phone companies already spend large sums to shape federal and state regulation. AT&T, for example, donated $200,000 last year to the Committee to Protect California Jobs, which campaigned against a California ballot initiative that would have allowed consumers to prevent technology companies from selling some of their personal information. It is not in the public interest to let T-Mobile and Sprint join forces, adding another Goliath to the ranks of tech companies.

The federal government has adopted a permissive attitude toward corporate mergers. Ajit Pai, chairman of the Federal Communications Commission, which also must approve the merger, publicly blessed the deal last month.