The Sony Xperia S is a fully PlayStation certified device, though at launch it lacked access to the PlayStation Store - not any more though. Sony just opened the doors and let the Xperia S and Xperia Acro HD (the Japanese version of the S), but the others of the NXT lineup will have to wait.
The placeholder app will download two new apps to your Xperia S (or Acro HD) - PlayStation Store, where you get games, and the PS Pocket, which serves as a launcher for games.