Need for Speed ProStreet (2007) on the PSP differs significantly from its home console counterparts. Due to the PSP's portable nature and lack of a persistent online server (post-GameSpy shutdown), the save data file ( ULUS-10362DATA or similar, depending on region) is critical for progression, customization, and car inventory.
Some popular cheats and exploits include: Nfs Pro Street Psp Save Data
If you're a fan of Nfs Pro Street Psp, make sure to save your data regularly and backup your save data to prevent any losses. Happy gaming! Need for Speed ProStreet (2007) on the PSP