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 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 monetize its mobile platform by featuring Facebook prominently on the phone.
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.
News of the April 4 event at social network's main campus in the Silicon Valley city of Menlo Park came as the research firm IDC released a Facebook-backed study showing that smartphones have become people's close friends in the US.
US smartphone owners tend to be connected from the instant they rise until they fall sleep and revel in every minute of it, according to the study.
A weeklong IDC survey of more than 7,000 people ranging in age from 18 to 44 years old with iPhones or Android-powered smartphones showed that four out of five check their handsets within 15 minutes of waking.
The top three applications used were for messaging; Web browsing, and Facebook, in that order, according to IDC.
"People have a universal need to connect with others, especially those they care deeply about," IDC researchers said.
"This coupled with mass market adoption of smartphones means that social engagement via phones has become mainstream."
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 onto smartphones and tablet computers, tailoring services and money-making ads for mobile devices.
"Now, we are a mobile company," Zuckerberg said at the conference.
Zuckerberg rejected suggestions that Facebook would make its own smartphone, adamant that the company had no intention of stepping into the fiercely competitive handset hardware arena.
"Apple, Google, everyone builds phones we are going in the opposite direction," Zuckerberg said at the time.
"We want to build a system deeply integrated in every device people want to use."