Facebook emailed invites Tuesday for a press event at its headquarters in Menlo Park, Calif., Jan. 15, but what is it all about?

The only clue the invitation offers is this sentence:

Come and see what we’re building.

Despite the social network’s repeated denials, speculation about a Facebook phone heated up following the announcement of the press event.

Facebook analytics provider Wisemetrics said in a blog post that it believes Facebook will unveil its social commerce strategy Jan. 15.

If “building” is taken literally, the social network could reveal details about its planned headquarters expansion.

Or it could be something else altogether.