Safari on iPhone has a number of things that are NOT implemented. Here’s a list of things that don’t seem to work (and I’ll be adding more as time goes on):
Javascript:

window.onmousedown
window.onclick
window.onscroll

CSS:

overflow:hidden
position:fixed
position:static
-webkit-column-*

If you find any more, please leave them in the comments and I’ll add them to the list.