T-Mobile USA is going after Verizon Wireless' claims that it uses spectrum more efficiently than other operators, a new line of attack in its fight to block Verizon's $3.9 billion purchase of nationwide AWS spectrum.

Verizon has told the FCC it is already using its spectrum more efficiently than other providers and "serves more customers per MHz than other national carriers," but even so will still run into spectrum shortages in some markets as early as next year.

Its purchase of AWS spectrum from four cable operators commonly referred to as “SpectrumCo” will address the shortage, Verizon said. But T-Mobile and other opponents to the deal said it will consolidate too much spectrum in the hands of a single operator.

T-Mobile government affairs executive Steve Sharkey this week sought to undermine Verizon's efficiency claims in a post on the operator's official blog.

"On average, T-Mobile is 50 percent more efficient than Verizon in the top markets," he said. "This is a very different picture than the one Verizon paints for the FCC and the public."

Sharkey argued that Verizon's calculations should have been conducted on a market-by-market basis, improperly included spectrum that T-Mobile doesn't yet have access to – the AWS airwaves gleaned from the failed AT&T merger – and failed to account for the fact that T-Mobile holds no spectrum below 1 GHz (beachfront airwaves that are more efficient than the spectrum above 1 GHz that T-Mobile holds).

Verizon replied that it had already "made a strong case that it is in the public interest to get SpectrumCo's previously unused spectrum into the hands of consumers" in filings with the FCC, where it has also refuted T-Mobile's claims.

According to Verizon's calculations, it serves 109 million wireless customer connections using an average of 89 MHz nationwide, with each megahertz of spectrum serving, on average, 1.23 million customers.

Once its AWS purchase closes, it would hold an average of 109 MHz nationwide, with each megahertz of spectrum serving, on average, nearly 1 million customers.

"Despite the claims of T-Mobile and others to the contrary, this usage makes Verizon Wireless the most spectrally efficient wireless provider currently and the second most spectrally efficient provider post-transaction (second only to AT&T and tied with MetroPCS)," Verizon said in a rebuttal filed with the FCC in early March.

Verizon wants to use the spectrum to add capacity to its LTE network, which uses its 700 MHz holdings. The deal is still being reviewed by the FCC.