SonicStage is the name for Sony software that is used for managing portable devices when they are plugged into a computer running Windows. It was first used in VAIO PCs put on the Japanese market in October 2001, and superseded OpenMG Jukebox. Version 2 was found on 2004 model products, and Version 3 on 2005 model products (Sony introduced native mp3 support on its music players in 2005).
SonicStage is a music file loader and library manager, similar to iTunes, Windows Media Player and Real Player. It is used to manage the library of ATRAC OMG and OMA recordings on a PC. The Sony Connect service is used to purchase recordings online, and can be accessed from within the SonicStage program - in much the same way that iTunes is integrated with the iTunes Music Store, Real Player is integrated with Rhapsody and so on.