Asp.net textbox won't show vertical scrollbar on iphone

I have an asp.net company site with text fields that can contain several hundred words. They display fine with a vertical scrollbar in Firefox and Safari on Mac. But in Safari on iphone (most users will have it) there is no vertical scrollbar. Is there a way to force a vertical scrollbar? If not, I suppose I will have separate pages with rich text boxes for iphone users.

Asp.net text boxes do not have a 'scrollbar' property. I've tried using the "overflow: auto" style, but that doesn't work either.