Rivals T-Mobile US and Verizon Wireless agreed a cash and spectrum swap deal worth $3.3 billion in a sign of how US operators are stashing stockpiles of airwaves for 4G.

Under one agreement T-Mobile US will pay $2.36 billion to Verizon Wireless for 15 licences in the lower 700 MHz part of the spectrum.

A second agreement, worth an estimated $950 million, will see Verizon Wireless transfer eight additional licences in the same band to T-Mobile US in exchange for licences in Los Angeles, San Francisco, Dallas, Atlanta and Detroit.

In addition, the two companies will realign spectrum blocks in certain markets, primarily in northern California and the Atlanta area.

The agreements enable both operators to fill in gaps in their respective footprints. T-Mobile US is hungry for low-band frequencies while Verizon Wireless needs more capacity to ease congestion in urban areas.

The 23 licences acquired by T-Mobile US include New York, Philadelphia, Atlanta, Los Angeles and Miami. It now has 700 MHz coverage in nine of the top 10 US markets.

The transactions need regulatory approval and are expected to close in the first half of 2014. T-Mobile US said it could launch services in the newly-acquired spectrum as soon as the fourth quarter of this year.

The 23 licences in the transaction were acquired by Verizon Wireless in a 2008 auction of lower 700 MHz spectrum.

Verizon Wireless began selling off the licences in May 2012. Nine companies, including T-Mobile US have purchased, or signed agreements to purchase, spectrum from the stockpile.

Verizon Wireless’s announcement does not name the nine (outside T-Mobile US) but said two are national operators, six are small or regional players and one is a minority-owned firm.

T-Mobile US signalled its intent to go into the market for more spectrum at the end of last year when it raised $3.8 billion through a stock sale and bond issue. At the time it was mooted that the new funds might be used for the purchase of Verizon Wireless’s 700 MHz spectrum.

However, a price of $3 billion was put on the purchase, indicating that T-Mobile US has paid slightly over the odds for its newly-acquired spectrum.