Word out of Silicon Valley this morning is that Yahoos board of directors has rejected a purchase offer from Microsoft, setting the stage for perhaps a larger battle over the future of the Internet giant. Microsoft is in a strong position; its offer of $31 was substantially higher than recent trading prices. But Yahoos argument is that given future growth projections, its stock is worth at least $40 a share.What happens next is anyones guess. Microsoft could implement a hostile takeover and buy up shares of Yahoo on the open market, or it could seek to replace Yahoos board with one that will accept the buyout offer. The wild card in all this is Google, the NY Times recently reported that Google had opened up discussions on a potential partnership meant to thwart Microsofts acquisition efforts.So what does this mean for the collaboration market? Its hard to say exactly, but there are a few possible outcomes. Should Microsoft acquire Yahoo it would likely have to divest at least a few key chunks of the combined business to avoid the wrath of US anti-trust regulators. Yahoo and Microsoft would control a large percentage of the hosted e-mail and instant messaging markets, and it wouldnt be surprising to see them forced to shed one or both businesses. AOLs instant messaging service suddenly becomes a much more valuable commodity (and perhaps Googles next target as Time Warner breaks up AOL?).The future of Zimbra is much cloudier. Yahoo acquired the competitor to Exchange/Notes as a way to position itself to compete with hosted SMB messaging/collaboration offerings from Microsoft and Google. Should Microsoft complete the acquisition of Yahoo, there doesnt appear to be much of a reason for Microsoft to keep Zimbra around. Would they sell off Zimbra, or shut it down to eliminate a potential competitor to Microsoft Office Live? The future of Yahoos other competitive offerings, such as Yahoo Travel, and Yahoo Groups is also up in the air until the situation around Microsoft is settled.Microsofts decision to spend $44 billion to buy Yahoo shows its serious to thwart Googles success in the search space, but the questions in my mind are what happens to Yahoos other services. Its going to a bumpy ride.