Facebook just sent out a round of invites to a mysterious mobile announcement event they’ll be hosting on Tuesday morning, and we just got ours.

The blogosphere seems to think it has something to do with the “long rumored Facebook phone,” as CNet’s Josh Lowensohn put it.

The fact that Facebook has repeatedly and flatly denied working on a phone hasn’t stopped Techcrunch, Gizmodo, and Mashable from all trying to put stock in the rumor.

It’s far more likely that it has more to do with recent rumors of a Groupon-like competitor tied into the brand new and hugely successful Facebook Places. While Places has just begun it’s phased rollout to the Facebook userbase, the usage of the service still exceeds the combined userbases of almost all the other location based services.

Matthew Ingram and Om Malik both speculated that this rumored Groupon move could have ties to the 30 million user-strong Places.

Mobile is clearly hot right now. Facebook is no stranger to mobile services, but the last couple weeks have brought a slew of announcements in mobile and security from players not thought of as primarily mobile players. Juniper, for instance, announced new security features to protect mobile users in an enterprise environment, which RIM and Android quickly copied this week (for full information, see our video coverage).

Whether it ends up being the fabled Facebook phone, something to do with group buying and location based services, or some other offering we haven’t yet imagined, we’ll be there and continuing to cover mobile like a blanket.