A day after rumors began to surface that Microsoft was in talks to acquire Yammer, a Facebook-like website that provides closed-circuit social networks for businesses, the two companies have allegedly settled on a deal. According to The Wall Street Journal‘s sources that are “familiar with the matter,” Yammer has agreed on a Microsoft purchase for the zinging price of $1.2 billion.

Yammer’s business-by-social network model would be be an immense boon to Microsoft’s own collaboration platform, SharePoint, which Yammer already integrates into its services. The social capabilities of SharePoint have been a slow development but simply incorporating Yammer instead of continuing to lag behind competing products could accelerate SharePoint to at least somewhere near the front of the class.

Yesterday, when news began to emerge that Microsoft was planning some big-time but very exclusive “media event” on Monday, speculation began to circulate that Microsoft’s big announcement was going to involve a Yammer acquisition. However, since news has begun to leak out that the deal may have already been sealed, that seems to belie any possibility that the Yammer purchase would be the centerpiece of Microsoft’s announcement next week.

If the acquisition is confirmed, this would mark the second large acquisition Microsoft has made in as many years. In 2011, Microsoft picked up the video-calling service Skype for the beefy price of $8.5 billion, the biggest acquisition in Microsoft’s history. The $1.2 billion price tag attached to Microsoft’s purchase is nearly two and a half times more than Yammer’s $500 million valuation that was reported in February of this year.

Neither company has released any official statement confirming the acquisition, but watch this space and we’ll update you as more information becomes available.