While the console versions are full 3D adventures, the PSP version appears to play on a 2D field, akin to Prince of Persia Classic. However, Vignola clarified a bit further, describing the game as a "3D sidescroller, because the world itself is 3D and we play with depth ... the Prince [is] not always locked onto an axis."
As with Assassin's Creed Bloodlines, The Forgotten Sands is promising connectivity between the PS3 and PSP versions of the game. By connecting the two, you'll be awarded bonus XP in the PS3 version and the original Sands of Time costume for the PSP version. Hopefully, the similarities with the PSP Assassin's Creed end there -- Bloodlines wasn't exactly a critical darling.
The PSP version of Prince of Persia: The Forgotten Sands will be available on UMD and PSN on the same day as its console counterparts: May 18.