Regulators rarely comment on specific deals (especially hypothetical ones), but it's not hard to read between the lines.
Not only would Sprint and T-Mobile have to persuade the Justice Department to bless their merger, but because the deal would involve the transfer of wireless airwave licenses, they would also need approval from the FCC.
FCC Chairman Tom Wheeler has indicated he would put any major wireless merger through the wringer.
"The mobile business is today with four carriers a competitive business," he said during a public discussion in Ohio in December. "And it's important it stay that way."
Even assuming opposition from the Obama administration, Sprint (and its parent company SoftBank) could try for the deal anyway and hope to win in court.
Sprint would have a stronger legal defense than AT&T did. Verizon and AT&T are the industry's largest firms, with Sprint and T-Mobile trailing far behind.
In a recent interview on Bloomberg Television, T-Mobile CEO John Legere argued that a merger with Sprint could help crack the industry's "duopoly" and actually lead to more robust competition.
But Jeffrey Silva, a telecommunications industry analyst with Medley Global Advisors, said that trying to beat the government in court would be a "huge risk" for Sprint.
"The signals seem to be pretty clear at this point that the administration does not want this deal," he said. "To just kind of hope that you can win in overtime with a federal judge, that's a really risky high-stakes game to play."
If Sprint tries to buy T-Mobile and fails, it would likely be on the line for a hefty breakup fee. A failed merger also ties up a company's resources in legal fees and lobbyists and can mean delaying other important business decisions.
Sprint and T-Mobile declined to comment for this story.
The Justice Department has argued that T-Mobile is a "maverick" competitor, shaking up the wireless industry by introducing new features and pricing plans. Last month for example, the carrier announced that it will pay the early termination fees for people who switch from a competitor.
"Pushed by T-Mobile, the competition has responded," the Justice Department's Baer said in a speech last week in New York, noting that Sprint recently unveiled a new unlimited data plan and that AT&T has hit back by offering a $200 credit to T-Mobile customers who switch. When T-Mobile announced a plan last year to allow customers to upgrade phones twice a year, the other carriers all responded with their own plans to allow more frequent upgrades.
"Competition today is driving enormous benefits in the direction of the American consumer," Baer said.
But Silva said the executives at Sprint and T-Mobile may be wondering how long they can compete with Verizon and AT&T.
"Both are trailing in 4G LTE build-out, and if you look at market share and subscribers, there's quite a bit of distance between themselves and AT&T and Verizon," he said.