The proposed 2011 deal, which would have seen AT&T pay $39 billion to take over T-Mobile USA, in the face of opposition from both the U.S. Federal Communications Commission and the Department of Justice. The two agencies, which faced pressure from carriers including Sprint, feared the takeover would harm competition.

"Last year, I was asked why did I, personally, and why did Sprint, take such a loud, strong, vehement opposition to the T-Mobile-AT&T deal," Hesse said during a keynote speech at Sprint's developer conference in San Jose.

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"I was concerned that if we had a government-sanctioned duopoly, investment would dry up," he said. "I think the $20.1 billion investment by Softbank into Sprint is validation of the way the Department of Justice and FCC looked at it."

Last week, Masayoshi Son, chairman and chief executive officer of Softbank, told Bloomberg News in an interview that he wouldn't have made an investment of "even $1,000" in the U.S. mobile market had the AT&T and T-Mobile deal succeeded.