There are several reasons why you might want to download Street Fighter 4 PSP ISO:

confirms it was released for PC, PS3, Xbox 360, 3DS, and mobile, but confirms no PSP version exists.

: Fan-made titles like Street Fighter Ultimate Collection are independent games built by the community to run on custom firmware.

is available on mobile stores. It features 32 characters and is even available for free to Netflix subscribers.

: If you must have SF4 on a portable device, Capcom's Official Mobile Port for Android and iOS is the closest experience to the original console game.