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⚠ A Tax Bill to Rearrange the LicencesLow threat

T-Mobile US (TMUS) — threat to the moat

T-Mobile's 800 MHz sale to Grain will raise cash taxes by about $850 million; trading spectrum costs real money.

Trading licences is not free. The sale of 800 MHz spectrum to Grain will raise T-Mobile's cash taxes by about "$ 850 million"1, because the licences sold carry a low tax basis. The licences in the deal were held for sale at about $3.6 billion2.

T-Mobile spectrum sales: proceeds and costs ($M)2,900Grain proceeds (cash)about 850Cash tax from Grain sale2,0003.45 GHz proceeds1513.45 GHz gainT-Mobile US Form 10-K FY2025, spectrum transactions
The tax bill is a large share of the Grain cash.

The gain on paper is small next to that. The 3.45 GHz sale produced a gain of $151 million on $2.0 billion3. A company that keeps swapping spectrum to tidy its holdings will keep paying tax on the old book values.

Tax is not a small line for T-Mobile in any case. It guides to an effective tax rate of 25% to 26% for 20264, after income tax of $3,289 million on pre-tax income of $14,281 million in 20255. A spectrum sale with a large gain adds cash tax on top of a rate that is already full.

The Grain sale is also a swap. T-Mobile receives Grain's 600 MHz licences as part of the price6, adding to the low band it has been buying from Channel 51 and Comcast. Part of the tax is the cost of trading spectrum it does not need for spectrum it does.

This matters because spectrum is the one asset T-Mobile cannot replace on demand. The swaps are sensible if the bands sold are genuinely spare. The test arrives with the cash: if spectrum-related cash taxes and new purchases together exceed the proceeds of sales in 2026, the rearrangement will have cost more than it raised.

References
  1. ReportedThe sale of 800 MHz spectrum to Grain will raise T-Mobile's cash taxes by about "$ 850 million", because the licences sold carry a low tax basis.
    T-Mobile US, Inc. Form 10-K for fiscal 2025 (year ended 31 December 2025) - spectrum: holdings by band, licence transactions and the spectrum roll-forward. — FY2025 · publ. 11 February 2026 · source ↗
  2. ReportedThe licences in the deal were held for sale at about $3.6 billion.
    T-Mobile US, Inc. Form 10-K for fiscal 2025 (year ended 31 December 2025) - spectrum: holdings by band, licence transactions and the spectrum roll-forward. — FY2025 · publ. 11 February 2026 · source ↗
  3. ReportedThe 3.45 GHz sale produced a gain of $151 million on $2.0 billion.
    T-Mobile US, Inc. Form 10-K for fiscal 2025 (year ended 31 December 2025) - spectrum: holdings by band, licence transactions and the spectrum roll-forward. — FY2025 · publ. 11 February 2026 · source ↗
  4. ReportedIt guides to an effective tax rate of 25% to 26% for 2026, after income tax of $3,289 million on pre-tax income of $14,281 million in 2025.
    T-Mobile US second-quarter 2026 results release, Form 8-K exhibit 99.1 - postpaid account additions, ARPA, Core Adjusted EBITDA, shareholder returns and raised 2026 guidance. — Q2 2026 · publ. 23 July 2026 · source ↗
  5. ReportedIt guides to an effective tax rate of 25% to 26% for 2026, after income tax of $3,289 million on pre-tax income of $14,281 million in 2025.
    T-Mobile US, Inc. Form 10-K for fiscal 2025 (year ended 31 December 2025) - consolidated financial statements, segment expense table, cash flow and capital returns. — FY2025 · publ. 11 February 2026 · source ↗
  6. ReportedT-Mobile receives Grain's 600 MHz licences as part of the price, adding to the low band it has been buying from Channel 51 and Comcast.
    T-Mobile US, Inc. Form 10-K for fiscal 2025 (year ended 31 December 2025) - spectrum: holdings by band, licence transactions and the spectrum roll-forward. — FY2025 · publ. 11 February 2026 · source ↗
Sources
Generated October 6, 2026