We have some additional confirmation directly from Samsung that they will not be debuting the Galaxy SIII at Mobile World Congress, just as they indicated previously. However, this time, they did share that the phone will be getting its own launch event sometime in the first half of this year, closer to when the product will actually hit shelves. Here's Sammy's quote,

“Samsung is looking forward to introducing and demonstrating exciting new mobile products at Mobile World Congress 2012. The successor to the Galaxy S2 smartphone will be unveiled at a separate Samsung-hosted event in the first half of the year, closer to commercial availability of the product.”
It's nice to see a company start to consider holding launch events closer to the actual release of their product. It gets frustrating waiting months on end after an OEM already "officially launched" a product. We'll see if Samsung actually holds to what they are implying.

Source: Phandroid