Set in Liberty City, in 1988 (a few years before Tommy Vercetti steps into the city in Grand Theft Auto III), you play as Tony Cipriani. There are a few changes to the city compared to Grand Theft Auto III. The missions are also shorter than the console counter-parts.
It was originally expected to be a PSP-only title, however a PS2 version has also been released. Whether it's available for the Xbox and PC, is not known.