Some people have said it is slow. I have a decent internet connection here and an iPhone 3Gs. Apart from the fact that, on entry the whole screen is re-drawn, it seems to work fine for me.
At the moment it is not possible to actually edit a Wave but viewing is OK.
- Enter the address https://wave.google.com/ into the iPhone Safari.
- You will see warning messages that the browser is not compatible... Ignore this warning and go ahead.
- Click the + on your phone and select Add To Homescreen.

You now have Google Wave at the click of a button on your iPhone.