Last week Google's CEO Eric Schmidt wrote to the Kevin Martin, Chairman of the FCC saying that they would bid a minimum of $4.6 billion if certain open platform conditions were included in the auction award.

But there are a couple of billion other reasons why Google prefers the 700 MHz spectrum.

The 700 MHz mobile network would be inexpensive to build compared to any other alternatives - GigaOM says:

"...The spectrum, currently owned by broadcasters, has been used for analog television. But it is set to be turned over to the government in 2009. Due to its broadcast-attractive physics (like its ability to penetrate walls), this spectrum is desirable for both broadband communications in general and public-safety uses in particular.

Also, a 700 MHz mobile network would be relatively inexpensive to build compared to the alternatives:

"...According to some estimates, the cost of building a nationwide wireless network over the 700 MHz spectrum is around $2 billion versus a nationwide 1900MHz PCS that costs approximately $4 Billion. The costs are lower in rural areas, due to less interference issues and wide-open spaces. That's because each tower broadcasting at 700MHz covers twice as many square miles. Some estimates say that a single 700 MHz tower can cover 20-miles. (#)(read more)