AT&T/T-Mobile

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AT&T in March 2011 announced plans to spend $39 billion to acquire T-Mobile, claiming the tie-up would produce cost synergies that exceeded the hefty sticker price. And it pulled out all the stops to close some kind of deal, including negotiating with Leap Wireless (which provided Cricket service at the time) to sell significant T-Mobile assets and exploring a network-sharing “Plan B” joint venture with T-Mobile rather than a full-on takeover.

In the end, though, the acquisition failed to gain the approval of federal regulators—the Justice Department even pursued a lawsuit on antitrust grounds—and by the end of the year AT&T finally pulled the plug on the effort. And that failure was costly.

AT&T had to pay a breakup fee worth $6 billion, including $3 billion in cash and a seven-year roaming agreement that allowed T-Mobile to expand its coverage by roughly 20%. Perhaps even more important was the AWS spectrum AT&T handed over to the smaller carrier in 128 markets, including 12 of the top 20 markets in the United States.

AT&T recovered, of course: It not only remains the second-largest carrier in the nation, but it’s moving aggressively into digital media and advertising with the $48.5 billion acquisition of DirecTV in 2015 and the pending buyout of Time Warner for $85.4 billion.

But the failed deal was transformative for T-Mobile, which handed John Legere the reins as CEO in September 2012, taking over for interim CEO Jim Alling. T-Mobile, which had been reeling, moved quickly to put its new AWS airwaves to work as it launched LTE in 2013, and the cash payday helped as parent Deutsche Telekom invested $4 billion in network upgrades.

T-Mobile expanded its LTE network to cover 230 million POPs by July 2014 as its footprint outgrew Sprint’s coverage, and a year later it passed Sprint to become the No. 3 mobile network operator in the United States.

"The company is not in need of doing something [in terms of a deal] to be successful in the short to medium term,” John Legere said at that time. T-Mobile’s astounding momentum since then has proven Legere right.

AT&T/T-Mobile