T-Mobile customers are in for a summer treat as the carrier just announced it has agreed to purchase 10 MHz of Advanced Wireless Services (AWS) spectrum for $308 million in cash from U.S. Cellular. The deal is still pending regulatory approval, but is expected to close sometime in the fourth quarter of 2013.

The spectrum expansion is crucial for T-Mobile, which has been eager to roll out its 4G LTE network coverage to more of its customers. The carrier said that the additional AWS spectrum would allow T-Mobile to roll out 4G LTE for another 32 million people in 29 key markets, mostly in the Mississippi Valley region. These include St. Louis, New Orleans, Louisville and Kansas City.

"In today's marketplace, spectrum is gold," said John Legere, President and CEO of T-Mobile, in a press statement. "This is a rare opportunity to secure precious AWS spectrum in key markets that will immediately be put to use by both T-Mobile and MetroPCS customers. This deal expands our network and capacity, allowing for a broader roll-out of 4G LTE and an even faster and more reliable 4G experience for our customers - in addition to spurring competition in the wireless marketplace."

Still, T-Mobile, which only recently switched on its 4G LTE network, has a lot of catching up to do before it is on equal footing with rivals AT&T and Verizon. According to the New York Times, AT&T has already deployed 4G LTE in 290 markets, while Verizon Wireless already offers the service in 500 markets.

T-Mobile had previously sought to narrow the gap between the scope of its LTE offerings and that of its competitors by merging with AT&T, however that deal was scuttled by the Justice Department and Federal Communications Commission amid antitrust concerns.  T-Mobile instead wound up merging with a much smaller carrier - MetroPCS - but even together, the two comprised only the fourth largest domestic cell carrier.