mysis and eussNL have discovered a method to enable PS2 software compatibility on PS3 consoles. This method allows newer PS3s to use the software-based emulator released with the second generation hardware.
Source: PS3 Development Wiki via PS3Hax
Getting Playstation 2 Software Emulator working
Method (on Firmware 3.55, without! Cobra-USB Dongle or Downgrade) for all consoles (fat & slim).
1. Replace following files on your consoles /dev_flash/
with the ones included in this archive
p3dwik-ps2compatfiles.rar
2. Get into Factory Service Mode (FSM Tool/Dongle)
3. Insert your Original PS2 Game Disc
4. It will run.
Note: Backups wont work. You're getting the compatibility of the 2.60 software emulator with all of its bugs.
Source: PS3 Development Wiki via PS3Hax