After 17 rounds, the 700MHz spectrum auction has finally hit its one of its most closely watched targets: bidding on Block C has surpassed the Federal Communications Commission's mandated $4.638 billion reserve, meaning that the FCC's mandated open access rules will come into play. Bids on the block of spectrum totaled $4.744 billion after Round 17.

Yesterday, the auction passed another significant milestone, crossing the FCC's $10.3 billion threshold for the auction as a whole. As of the end of Round 17, total bidding stood at $12.789 billion. With the threshold crossed, the auction is all but certain to come to a successful conclusion, meaning that we won't have a replay at some point in the future.

The identity of the high bidder on Block C (or any other block, for that matter) remains unknown, as the FCC's auction rules require bidders to remain anonymous. Speculation about who is behind the action on Block C has focused primarily on AT&T, Google, and Verizon, with many analysts believing that Google will drop out of the bidding once the reserve price has been reached.

Block D, which is a nationwide license that will be used for both a public safety and commercial network, has gotten no interest from bidders since an opening bid of $472 million in the first round. The reserve on that block is $1.33 billion. If it's not met, the FCC would have the option of accepting the highest bid or holding another auction, perhaps with fewer restrictions on the spectrum.

The rest of the licenses are regional, and bidding on most of those appears to be brisk, with regional licenses going for as much as $429.4 million.

There's no set end date for the conclusion of the auction; the FCC will stop it once bidding grinds to a halt. If you want to follow along at home, the FCC's results page is updated within 10 minutes of a round ending.