I am hoping to find out how often, on average, companies or
organizations change the menu trees that are in their IVR (interactive
voice response) systems.  

Specifically I am interested in Customer Service related IVR menus
(Such as that which you would find when you call the phone company and
hear "Press 1 to pay your bill, Press 2 to get your balance, etc" ).

The key for me is to find out how often and, if
possible, to what exent, the menu tree options are changed.