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AT&T Inc. (NYSE: T) tried to buy T-Mobile US Inc. (NASDAQ: TMUS) in 2011. Regulators balked and the $39 billion deal cratered. With a possible tie-up of Sprint Corp. (NYSE: S) and T-Mobile a new possibility, deal-hungry AT&T may reappear to reverse its largest M&A failure.

Reuters reported that Sprint’s majority shareholder, Softbank, might give up its control over the telecom in exchange for a favorable transaction with Deutsche Telekom controlled T-Mobile. Nearly three years ago, a similar potential combination ran into regulation skepticism. Will that change? If it does, the door could be open for AT&T.

One of the most attractive aspects of the T-Mobile business is that the number three U.S. wireless carrier has added subscribers at an impressive rate, passing Sprint, which now sits in the number four position. Currently, T-Mobile has about 68 million subscribers to Sprint’s 58 million, and AT&T’s 132 million and Verizon Communications Inc.’s (NYSE: VZ) 142 million. The market for wireless services is saturated. Nothing other than a buyout will significantly change the landscape.

AT&T is on an M&A run nearly unprecedented in recent U.S. financial history. It already has bought DirecTV for $49 billion. It has offered $85 billion for Time Warner Inc. (NYSE: TWX). A buyout of T-Mobile would cost another $70 billion. AT&T would not only have to convince regulators the deal would not hurt consumers. It would need to get Wall Street to accept the proposition that it can use its balance sheet, savings from an AT&T combination with T-Mobile and the cash flow from what would be a massive telecom, satellite and entertainment company to support a huge mountain of debt. Anxiety about finances might scuttle the plan, even if it makes sense on paper.

There is another possibility. Verizon has been left behind in terms of transmission operations like satellite and integration with a large content company like Time Warner. Maybe the AT&T deal with T-Mobile deal is the wrong possibility to look at …