A merger of T-Mobile and Sprint would make the combined carrier “the dominant spectrum holder” in some key markets across the United States, according to the network-tracking firm Mosaik.

The operators are expected to announce a proposed tie-up very soon—perhaps even in the next few days—and spectrum will play a key role in any deal. T-Mobile has already begun to launch service on some of the 600 MHz spectrum for which it paid nearly $8 billion at auction earlier this year, and Sprint owns more high-band spectrum than any other U.S. carrier, according to data from Allnet Insights & Analytics.

A merger would provide the combined carrier with a huge weapon to take on Verizon and AT&T in rural markets, Mosaik said last month. But those airwaves would also be a significant advantage in urban areas, as evidenced by this map illustrating carriers' current holdings.

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“We all know that a Sprint/T-Mobile merger would have significant impact on the industry, but the extent of the total spectrum ‘script flip’ cannot be overstated,” said Andrew Miceli, Mosaik’s vice president of global sales, in an emailed statement to FierceWireless. “The new Sprint/T-Mobile company would move to the dominant spectrum holder across a majority of the nation, including many major metropolitan markets. With efficient use of the spectrum, deploying new technologies to support multiband carrier aggregation and the latest handsets to support these bands, the combined company has the capability to take the lead in both coverage quality and capacity on a national level.”

Indeed, the spectrum holdings of T-Mobile and Sprint appear to be remarkably complementary. Sprint’s 2.5 GHz airwaves are highly prized for their ability to transmit large amounts of data quickly, but because they don’t propagate as well as lower bands, they require a highly densified network. Sprint also owns sizable chunks of 800 MHz and 1900 MHz spectrum.

T-Mobile’s new 600 MHz spectrum, on the other hand, is ideal for increasing coverage in the suburban and rural markets into which the carrier is expanding. A merger would enable the combined carrier to continue to grow its overall network footprint, then, and lay the foundation for increased capacity in urban areas:

“Sprint is extremely well-positioned with respect to theoretical capacity, given their rich 2.5 GHz holdings, and the increases they have enjoyed and will enjoy in spectral efficiency gains from refarming to LTE, and also spectrum reuse and further efficiency gains through MIMO—something particularly conducive to the smaller wavelengths of 2.5 GHz, as well as HPUE,” Craig Moffett of MoffettNathanson wrote earlier this year. “That said, we remain concerned about the usability of Sprint’s 2.5 GHz network, notwithstanding improvements in spectrum efficiency in this band. More significantly, we have ongoing concerns regarding the company’s liquidity and therefore their ability to meaningfully invest in their network and appropriately realize the theoretical potential of their 2.5 GHz spectrum trove, as it would be very expensive to do so.”

T-Mobile’s deep pockets coupled with Sprint’s spectrum assets could prove formidable in a market that—while increasingly competitive—is still largely dominated by Verizon and AT&T.