AT&T and T-Mobile are both eyeing valuable spectrum that Verizon Wireless holds but isn't currently putting to use, according to a report from The Wall Street Journal. The spectrum in question comes from the 700MHz A-block. Verizon paid $2.4 billion for the licenses to those airwaves, which offer better building penetration than higher frequencies, but the largest US carrier hasn't yet put the spectrum to use. In fact, it's long been open to the possibility of a sale — for the right price.

"The A spectrum is out there, and if someone walks up to me with an offer, we will entertain it," Verizon CFO Fran Shammo has said. "This is not a fire sale though, so if we don't get the right offer, we'll deploy the spectrum in our own network." Interference is also seen as a hindrance in building out 700MHz A-block spectrum. The A-block is thought to be vulnerable to interference from nearby TV operators using channel 51.

The rivals may soon square off

Rounding up more spectrum remains a top priority for T-Mobile. The company has raised $4 billion through a stock sale and by selling debt, money it says will be used to bolster its network with more spectrum. Fierce Wireless last month reported T-Mobile's interest in the A-block. AT&T has attempted to temporarily solve its own spectrum crunch through acquisitions; the carrier announced it would be buying Leap Wireless (along with its spectrum holdings) back in July. But its apparent interest in Verizon's airwaves suggests it's exploring as many solutions as possible.