I was updating some code on a Yahoo hosted site, and it wasn’t working because Yahoo will default you to PHP4 on their hosting. My code of course requires PHP5.
I spent a fair amount of time searching around for an answer and finally found it at http://help.yahoo.com/l/us/yahoo/smallbusiness/webhosting/php/php-38.html
I was surprised at how difficult it was to find this switch option! After I made this post, Yahoo support replied to give me the proper link and some more information, which I must compliment Yahoo support for doing.