The election of President Donald Trump and the appointment of Ajit Pai to run the FCC give Son an opportunity to try again.
But to win their blessing, Son must prove that the benefits of the Obama administration's decision to maintain a four-player market — lower prices, competition, unlimited data packages — can't last much longer.
Sprint has had to mortgage assets and cut billions of dollars in costs just to stay solvent, and must now compete for new subscribers with profit-draining price cuts and promotions.
While consumers may enjoy Sprint's five-line unlimited plan for a paltry $18 a line, the company hasn't had a profitable year in almost a decade.
"We can ride this capacity race pretty nicely compared to other players," Chief Financial Officer Tarek Robbiati said this month at an investor conference. "In the longer run, is unlimited a sustainable proposition? Probably not."
Under Chief Executive Marcelo Claure, Sprint ended seven straight years of subscriber losses. The introduction of half-off prices and $5 iPhone leasing broke that streak, but it didn't keep the company from falling behind T-Mobile to last place among the top four providers.
The loans have kept Sprint afloat as the Overland Park, Kan.-based company tries to generate cash. The woes have meant deep cuts to network spending and a focus on a lower-cost technology that will put a vast trove of 2.5 gigahertz spectrum to better use.
While Sprint has struggled, T-Mobile has sharpened its image as the underdog challenger to Verizon Communications Inc. and AT&T Inc., further complicating any transaction.
Armed with billions of dollars in breakup-fee money and spectrum courtesy of AT&T following the collapse of their merger in 2011, T-Mobile has been the biggest disruptive force in wireless, offering features like free video streaming, carryover data and low prices.
An an investor conference this month, T-Mobile CFO Braxton Carter agreed that the regulatory environment is now more conducive to mergers in the wireless industry.
But T-Mobile has become the fastest-growing U.S. carrier, and can sustain itself, he noted. If there were a potential deal, Carter said it would require "a very significant breakup fee."
There aren't any current talks between Sprint and T-Mobile — they're actually forbidden. SoftBank can't yet talk to T-Mobile's parent company, Deutsche Telekom AG, because of a gag rule related to an auction of U.S. airwave licenses. Sprint and T-Mobile declined to comment for this story.
For Son, the pressure to build scale isn't easing. Sprint is part of Son's famed plan to build a business empire that can endure for centuries.
His best argument may be that Sprint would never be a robust fourth competitor if left alone, and that putting the carrier and T-Mobile together would benefit consumers by bolstering a stronger third competitor to Verizon and AT&T.