A Gamestop page lists the PSP game Ratchet & Clank: Size Matters as getting a PlayStation 2 release in February 2008.
After first porting Syphon Filter: Dark Mirror from PSP to PS2, Sony is now supposedly porting the former PSP exclusive to the PS2. Grand Theft Auto: Liberty City Stories also did the same thing and rumors say Silent Hill: Origins will be ported too. — Via PSPfanboy