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.