According to a new government filing from U.S. Cellular, the nation’s fifth largest wireless network operator submitted bids for a minimum amount of $327 million during the FCC’s 600 MHz incentive auction of TV broadcasters’ unwanted spectrum.

“With the completion of the Clock Phase of the auction, U.S. Cellular is now committed to purchase 600 MHz spectrum licenses on which it submitted bids for a minimum amount of $327 million, subject to increase as the FCC completes the Assignment Phase of the auction, which is pending,” the operator wrote in a filing today with the U.S. Securities and Exchange Commission. “U.S. Cellular expects to be obligated to pay for the total committed amount, less the $143 million upfront payment made in June 2016, in the second quarter of 2017. U.S. Cellular currently expects to make such payment using cash on hand and/or borrowings under its revolving credit agreement.”

Forward bidding in Stage 4 of the FCC’s incentive auction came to an end late last week with bidders committing $19.63 billion for TV broadcasters’ airwaves.

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However, U.S. Cellular’s filing is somewhat noteworthy considering that the auction is now moving into the assignment phase, during which bidders will haggle over specific blocks of spectrum in each market. (Previous bidding was limited to generic chunks.) The FCC has said it won’t release the names of winning bidders for a few more weeks, and the quiet period remains in place. Those rules prevent bidders like U.S. Cellular from discussing the results as well as barring them from negotiating deals based on the spectrum.

This is unexpected. $USM just disclosed their winning FORWARD bids even though @FCC spectrum auction is not over. https://t.co/gKKtcvdMzL — Walt Piecyk (@WaltBTIG) February 16, 2017

A representative from U.S. Cellular said only that the filing "was required by SEC regulations."

Verizon, AT&T and T-Mobile were among the dozens of bidders in the auction—Sprint opted to sit out the event—and others included Comcast, Dish Network and smaller wireless carriers. Piecyk noted via Twitter that only 3% of available spectrum was left on the table.

U.S. Cellular was the nation’s fifth-largest wireless operator in the third quarter of last year, with around 5 million customers.

Article updated Feb. 16 with commentary from U.S. Cellular.