When it comes to conferences, the pre-show is often just as important as the opening day, if not more so. Mobile World Congress in Barcelona is no exception.

Day 0 has already proven Android's virility with five Android 2.3 Gingerbread smartphone announcements and two Android 3.0 Honeycomb tablets, with much more to come.

Even before a trio of press conferences from Samsung, Sony Ericsson, and Nokia got underway, LG announced its 9-inch, dual-core Optimus Pad tablet and spilled more beans on the Optimus 3D smartphone, a lens-less way to view 3D media.

A few hours later, Sony Ericsson surprised no one by officially unveiling the leaked--and even advertised--Xperia Play PlayStation phone during its press conference, but not everyone is impressed. The phone-maker also confirmed the Xperia Neo and physical keyboard-toting Xperia Pro, and sat down with CNET to discuss its aspirations to become the top Android maker in the world.

Samsung also delivered its expected news of its next-generation Galaxy S II smartphone and dual-core Galaxy Tab 10.1.

Nokia already made a splash with last Friday's announcement that it will abandon its proprietary smartphone operating systems in favor of Microsoft's Windows Phone 7 platform. Although Nokia didn't have product news, CEO Stephen Elop answered journalists' questions about the dramatic partnership.

All in all it's been a busy day for CNET's jet-lagged crew. Stay tuned for more in-depth analysis and hands-on reviews to come out of Barcelona this week.