LAS VEGAS -- After delivering the keynote address at CES tonight, Microsoft CEO Steve Ballmer headed across town to speak during Sprint's unveiling of its new "Overdrive" 3G/4G Mobile Hotspot.

Here's the odd thing about that: It wasn't really clear why he was there.

When plans for the event were announced last month, there was some speculation that Ballmer would be there to announce a new Windows Mobile WiMax phone in conjunction with Sprint. Instead, Ballmer spoke generally about the benefits of pervasive connectivity, and how it would help enable Microsoft's "three screens and a cloud" strategy of connecting PCs, TVs and mobile devices.

Sprint Overdrive

A Sprint representative said afterward that Ballmer was there because of the role Microsoft plays in a range of devices (Xbox 360, Zune, PCs, etc.) that will work in conjunction with the Overdrive. But that alone doesn't make a whole lot of sense, since the mobile hotspot will provide connectivity to pretty much any wireless-enabled device. In that context, just about any tech executive could have played the part.

So does Ballmer's appearance signal something bigger between the companies? Neither will say. And Sprint CEO Dan Hesse, the Seattle wireless veteran, didn't offer any clues in his remarks about any Microsoft role, or say anything that would suggest a closer relationship between the two companies.

Sprint is pitching the Overdrive device as a primary means of getting home and mobile broadband access, potentially replacing existing broadband services in the home, while letting people take the hotspot with them, as well. The company, which leverages the WiMax network of Kirkland-based Clearwire, says it will sell the device beginning Jan. 10 for $99.99 after a $50 mail-in-rebate, with a two-year service agreement.

Yes, in case you were wondering, that is comedian Frank Caliendo -- known for his John Madden impression -- introducing Ballmer at the beginning of the video above. And no, unfortunately, Caliendo didn't do an impression of Ballmer.