Shortly after the Facebook invitation went out for the April 4 event, the technology news site TechCrunch reported the announcement would be a modified version of the Google Android operating system with "deep native Facebook functionality".
Another report on "9 to 5 Google" said Facebook was designing the software for the new smartphone, which would be made by Taiwan's HTC.
Facebook's invitation said only "Come See Our New Home On Android".
The reports, if accurate, could explain the long speculation about a "Facebook phone" to help the social network better monetise its mobile platform by featuring
Facebook prominently on the phone.
At a TechCrunch Disrupt conference in San Francisco in September, Facebook co-founder Mark Zuckerberg said the social network giant is focused on mobile devices.
"It is really clear from the stats and my own personal intuition that a lot of energy in the ecosystem is going to mobile, not desktop (computers)," Zuckerberg said during an on-stage interview.
"That is the future," he continued. "We are going to be doing killer stuff there."
Facebook has made a priority of following its more than one billion members on to smartphones and tablet computers, tailoring services and money-making ads for mobile devices.
But Facebook has long held firm it has no intention of building its own smartphone, saying instead it would rather weave access to the social network into software running the gamut of handsets.
"Apple, Google, everyone builds phones -- we are going in the opposite direction," Zuckerberg has been quoted as saying. "We want to build a system deeply integrated in every device people want to use."