uhm.. I just sent you a PM we were started with the idea to make it compatible starting from iPhone 3GS and iPod 4G. We tried it on an iPhone 3G, and it resulted quite unplayable.. yes you can run it, but with a veery slow frame rate.. So thanks a lot for let us know!
Not sure about the iPhone 3G, but as I mentioned in my PM it runs really well on my iPod Touch 2G. Just some occassional slowdown, but I'm amazed at how fluid it is for as fast as the game is and with the quality of your graphics. Just thought I'd post those findings here so anyone with a 2G gives it a shot.