We know what Sprint/Clearwire needed: cash to fund a new, massive greenfield WiMAX network.

But what did Google, one of the surprise investors in yesterday’s deal, get for its $500 million investment? And was it something that the service providers in the equation should have been so willing to "sell off"?

Here’s exactly what Google gained for its half a billion bucks, from the press release on the deal:

• Google will “partner” with Clearwire on advertising services and applications.
• Google will be the “preferred” search provider and “preferred provider of other applications” for the new Clearwire retail product
• Google will partner with Clearwire on “an open Internet business protocol” for mobile broadband devices, at least in part driven via Google’s Android mobile operating system project
• Google will become the “default provider” of Web and local search services for all Sprint mobile services
• Sprint will preload Google services, including Google Maps for mobile, Gmail and YouTube on select phones

While much of those deals are for placement on a network that doesn’t exist yet, Google also gains access to Sprint’s existing wireless customer base. And it gains access to all of those customers in a broad array of areas, including regular search, local search, map-driven search, mobile applications and more.

“Google is an extremely savvy player. But what we’re seeing now is a watershed moment in Google’s existence,” said Roger Entner, senior vice president at consultancy IAG Research. “Until now, they’ve put themselves in the ‘do-no-evil’ category, where they were here to help everyone else while making billions on the side. Now they’re becoming much more involved with others and almost becoming a power broker. Five hundred million dollars for what they are getting is a steal, especially when it includes the Sprint handset.”

Indeed, for all its talk about openness, the main thing Google bought -- and a move it has ridden to success on the Web -- is preferred search-provider status.

Preferred is more “open” than “exclusive,” but as it has shown in deals with Mozilla/Firefox, MySpace and others on the Web, for Google, it’s the next best thing. That’s why it’s already cut deals with Apple and Nokia to be the search box on their devices.

“Google knows the game better than everybody else and somehow gets them to play by their rules,” said analyst Entner, who encouraged service providers not to get “blinded by the Google brand name” but instead work with multiple mobile ad partners. “In wireless, everything is still up for grabs. What Google understands better than anybody else right now is how weak they actually are in wireless. They are playing that expertly. After negotiating with them, [service providers] should check their pockets to see if they have anything left.”

Not all analysts agree that Clearwire got "taken."

"Overall this is a smart move," said Philip Solis, analyst at ABI Research. "Sure, mobile operators can continue trying to retain control of different aspects of the ecosystem of which they are not experts in, but this will eventually be to everyone's benefit. The new Clearwire network will do what it does best - providing mobile access to the Internet. Some people may use the term "dumb pipe" here, but that is a negative and misleading way to look at it. They are providing mobile access to the Internet and partnering with others to provide what they see as a superior service. In short, the new Clearwire is giving up something to gain a whole lot more."