Michael Arrington of TechCrunch is reporting that Yahoo! has paid $350 million to purchase Zimbra. The official announcement isn't expected until this evening, but Arrington's in a pretty good position to pick up gossip today. He's hanging out with a ton of industry insiders today at a little software conference Arrington put together with Weblogs Inc. founder Jason Calacanis called TechCrunch40.

So we're going to assume his information is good and enter the world of wild speculation.

Zimbra makes some impressive open source communication tools for online/offline use. The company has a powerful e-mail client, calendar, and VoIP features.

While it's unlikely that Yahoo! plans to completely overhaul its e-mail client yet again, we could see Zimbra features showing up in Yahoo! services. Particularly the slick AJAX interfaces, the powerful collaboration tools, and the online/offline functionality.