A friend tried it on his 2g iphone and got 15 minutes battery life. Useful as a proof of concept. or as engineering work in progress, but not as a phone.
Just tried it. Very slow. Very hot. Seems like there's still no GPU support and very little power management.
Camera and video doesn't work. Also it seems like you can connect to internet only via WiFi. As for the speed, it runs ok on iPhone 3G