I've got a simple responsive top menu that collapses on smaller screens: http://versastudio.com
It works fine when I resize the window on Firefox/PC and other PC browsers, however, clicking 'menu' does not toggle it open/closed on iOS 4.35 and older.
The js is here: http://versastudio.com/scripts/master-responsive.js
See the navCollapse function.
Hopefully people involved with developing for mobile devices, will have some answers for you here.