Mark Zuckerberg addresses the media and analysts today in Palo Alto.

PALO ALTO, CA--Let's get it over with. There is no Facebook phone. Mark Zuckerberg made that abundantly clear with a firm denial at a Facebook mobile event today at company headquarters in Palo Alto. But Facebook did announce a single sign-on.

Single sign-on is roughly an extension of (and replacement for) services like Facebook Connect, connecting you to third-party social apps and services. If you're already logged on to Facebook on your mobile phone, you'll be able to sign in to other apps using your Facebook credentials.

Groupon's Mihir Shah, vice president and general manager of mobile, demonstrated single sign-on on Groupon's mobile app, a service that offers people in certain cities local deals. Like clockwork, he signed in using his Facebook credentials. Zynga also showed off a poker app that worked the same way.

Other single sign-on partners include Yelp, Flixster, Loopt, BooYah, and Scvngr.

While it appears like a simple measure, single sign-on may dramatically reduce the amount of typing and tapping you do on a mobile phone. However, Facebook will need to address how it will keep malicious apps from delivering dangerous payloads to unsuspecting users through single sign-on. The company will likewise have to contend with users who would prefer to keep Facebook in the dark about their individual comings and goings on partner sites and apps.

Stay tuned for more news and analysis throughout the day, and check out our live blog for even more details.