The iPhone DevTeam hasn't released a jailbreak for the iPhone 3GS as of the moment but that won't stop famed iPhone homebrew developer ZodTTD for porting his emulators to the speedy new iPhone. Here we have a video preview of his two popular emulators, the gpSPhone and the psx4iphone running on the new iPhone 3GS.
On the first video, Zod previews the GBA emulator, gpSPhone, running on the iPhone 3GS. The video shows the emulator running at a minimum 150 FPS and maxing out at about 225 FPS, with sound and 0 frameskip whereas the iPhone 3G needed frameskipping just to reach 60 FPS.
On the second video, you have the Playstation emulator, psx4iphone running on 3GS. The video shows the classic PS1 game Final Fantasy 7 running at full speed at the very least without sound. Zod says that the build is still rough around the edges, as you can t switch games without restarting the emulator, and only the memory card saves are currently working, no save states just yet. Both these issues are being worked on. Stay tune for updates.