So Who's Not Bidding in the 700MHz Auction?

So far cable companies are not:

Today is the application filing deadline to participate in the auction.

One question is: will carriers participate partly to run the price up for someone like Google? AT&T recently bought a big chunk of bandwidth ($2.5 billion worth) from Aloha Partners. So it's not clear the number two US carrier will participate. Verizon, however, is more likely to do so.

Update: The four bidders so far appear to be Google, Cox Communications (the only cable provider), Frontline Wireless and AT&T.