“People don’t understand what they’re talking about,” Microsoft CEO Steve Ballmer told the Financial Times, referring to speculation about a post-Yahoo buying spree. “At the end of the day, this is about the ad platform.”

And don’t forget Google (GOOG) …

Now that investor-tormentor Carl Icahn has filed a proxy slate to unseat Yahoo’s board with the intent, one way or another, to push the company back into merger negotiations with Microsoft (MSFT), an obviously panicked Yahoo (YHOO) is scrambling to pull together a search-ad deal with Google (GOOG).

The possibility of a search-ad outsourcing arrangement between the two companies was, in part, what caused Microsoft to lose its appetite for Yahoo. Could it cause Icahn to lose his as well? Seems doubtful. Even if, as sources close to the situation tell the New York Post, the deal is the sort of open-to-all-comers arrangement Yahoo and Google hope would pass regulatory scrutiny. Under its terms, a real-time auction system would be used to select the most lucrative ads for a given search query from among those sold by Yahoo, Google or anyone else that cares to participate. Structured in this way, the deal might not, as Microsoft has claimed in the past, consolidate over 90% of the search-advertising market in Google’s hands and draw the ire of antitrust regulators.

Instead it might consolidate, oh say … 89.99% in the search sovereign’s hands. Said Kevin Lee, chairman of search engine marketing firm Did-It, “Given the way the ecosystem is put together now, Google would probably be the winner in a vast majority of cases.”

Here’s the full text of Microsoft (MSFT) CEO Steve Ballmer’s letter to Yahoo (YHOO) CEO Jerry Yang.

Mr. Jerry Yang
CEO and Chief Yahoo
Yahoo! Inc.
701 First Avenue
Sunnyvale, CA 94089

Dear Jerry:

After over three months, we have reached the conclusion of the process regarding a possible combination of Microsoft and Yahoo.

I first want to convey my personal thanks to you, your management team and Yahoo’s Board of Directors for your consideration of our proposal. I appreciate the time and attention all of you have given to this matter, and I especially appreciate the time that you have invested personally. I feel that our discussions this week have been particularly useful, providing me for the first time with real clarity on what is and is not possible.

I am disappointed that Yahoo has not moved toward accepting our offer. I first called you with our offer on Jan. 31 because I believed that a combination of our two companies would have created real value for our respective shareholders and would have provided consumers, publishers and advertisers with greater innovation and choice in the marketplace. Our decision to offer a 62% premium at that time reflected the strength of these convictions.

In our conversations this week, we conveyed our willingness to raise our offer to $33 per share, reflecting again our belief in this collective opportunity. This increase would have added approximately another $5 billion of value to your shareholders, compared to the current value of our initial offer. It also would have reflected a premium of over 70% compared to the price at which your stock closed on Jan. 31. Yet it has proven insufficient, as your final position insisted on Microsoft paying yet another $5 billion or more, or at least another $4 per share above our $33.00 offer.

Also, after giving this week’s conversations further thought, it is clear to me that it is not sensible for Microsoft to take our offer directly to your shareholders. This approach would necessarily involve a protracted proxy contest and eventually an exchange offer. Our discussions with you have led us to conclude that, in the interim, you would take steps that would make Yahoo undesirable as an acquisition for Microsoft.

We regard with particular concern your apparent planning to respond to a ‘hostile’ bid by pursuing a new arrangement that would involve or lead to the outsourcing to Google of key paid Internet search terms offered by Yahoo today. In our view, such an arrangement with the dominant search provider would make an acquisition of Yahoo undesirable to us for a number of reasons:

–First, it would fundamentally undermine Yahoo’s own strategy and long-term viability by encouraging advertisers to use Google as opposed to your Panama paid search system. This would also fragment your search advertising and display advertising strategies and the ecosystem surrounding them. This would undermine the reliance on your display advertising business to fuel future growth.

–Given this, it would impair Yahoo’s ability to retain the talented engineers working on advertising systems that are important to our interest in a combination of our companies.

–In addition, it would raise a host of regulatory and legal problems that no acquirer, including Microsoft, would want to inherit. Among other things, this would consolidate market share with the already-dominant paid search provider in a manner that would reduce competition and choice in the marketplace.

–This would also effectively enable Google to set the prices for key search terms on both their and your search platforms and, in the process, raise prices charged to advertisers on Yahoo. In addition to whatever resulting legal problems, this seems unwise from a business perspective unless in fact one simply wishes to use this as a vehicle to exit the paid search business in favor of Google.

–It could foreclose any chance of a combination with any other search provider that is not already relying on Google’s search services.

Accordingly, your apparent plan to pursue such an arrangement in the event of a proxy contest or exchange offer leads me to the firm decision not to pursue such a path. Instead, I hereby formally withdraw Microsoft’s proposal to acquire Yahoo.

We will move forward and will continue to innovate and grow our business at Microsoft with the talented team we have in place and potentially through strategic transactions with other business partners.

I still believe even today that our offer remains the only alternative put forward that provides your stockholders full and fair value for their shares. By failing to reach an agreement with us, you and your stockholders have left significant value on the table.

But clearly a deal is not to be.

Thank you again for the time we have spent together discussing this.

Sincerely yours,
/s/ Steven A. Ballmer

Steven A. Ballmer
Chief Executive Officer
Microsoft Corporation

Meanwhile, “people familiar with the matter” say that Yahoo (YHOO) may launch something in the next few days as well: a deal to carry search advertisements from Google (GOOG) alongside Yahoo search results. Such a deal would likely not be the sort of broad pact over which Microsoft has preemptively cried foul, but a non-exclusive arrangement open to the companies’ competitors as well. Under its terms, a real-time auction system would be used to select the most lucrative ads for a given search query from among those sold by Yahoo and Google. Microsoft too, if it were willing to participate.

The Internet portal will soon begin a “limited” two-week test of Google AdSense with an eye toward a broader search-ad outsourcing arrangement. That said, this tentative first step is by no means a harbinger of a larger deal. “… The testing does not necessarily mean that Yahoo will join the AdSense for Search program or that any further commercial relationship with Google will result,” Yahoo said in a statement.

It certainly doesn’t. Not if Microsoft has anything to say about it. In a hastily issued statement Brad Smith, Microsoft’s general counsel, cried monopoly over the exploratory alliance.”Any definitive agreement between Yahoo! and Google would consolidate over 90 percent of the search advertising market in Google’s hands,” Smith said. “This would make the market far less competitive, in sharp contrast to our own proposal to acquire Yahoo! We will assess closely all of our options. Our proposal remains the only alternative put forward that offers Yahoo! shareholders full and fair value for their shares, gives every shareholder a vote on the future of the company, and enhances choice for content creators, advertisers, and consumers.”