Yesterday, the CEO of T-Mobile’s parent company — Germany’s Deutsche Telekom — suggested in an interview that the insurgent “Uncarrier” is using a business model that’s “unsustainable,” to which T-Mobile US CEO John Legere responded in a tweet today: “It’s total bullshit.”

Deutsche Telekom CEO Timotheus Höttges “admitted that T-Mobile’s current approach is not sustainable,” according to Re/code, which published the interview. “The question is always the economics in the long term … and earning appropriate money,” Höttges said. “You have to earn your money back at one point in time.”

T-Mobile and its parent are investing $4 billion to $5 billion each year to stay competitive with AT&T and Verizon in the U.S. Meanwhile, Verizon and AT&T plan to make sizable investments in wireless spectrum, which may give them a bigger edge in service speed and coverage over T-Mobile.

Deutsche Telekom uses a slightly more refined public relations approach than Legere. (Imagine someone named Timotheus saying the word “bullshit,” even in private.) But Höttges did give Legere props for being fiercely competitive.

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“His management style will never be adaptable to Germany,” Höttges said, but added:

“I like people being disruptive… I like people who are brave. He is very much fitting to our DNA, how we want to be, even if he is very American in his approach.”

T-Mobile’s Uncarrier model is billed as the alternative to the usurious pricing practices traditionally used by the big U.S. wireless carriers. Things like contracts and data costs. Legere and company recently announced that most T-Mobile customers would be able to “roll over” unused data from month to month, although analysts told VentureBeat that the new program is more style than substance.

Hat tip: 9to5Mac